refactor(app/outbound): remove status counters from NewRecordResponse

[cratelyn]

nb: this branch is based upon #4299, and #4298.

in #4299 we made some prepatory
adjustments to the outbound proxy's route-backend metrics layer, and in
#4298 we introduced a new
linker-http-prom::status metrics layer that can be used to count response
status codes, in a manner that is agnostic with respect to the particular
protocol that instrumented traffic is using.

this branch performs a sequences of changes oriented towards two concrete
goals: 1: integrate the NewRecordStatusCode middleware into the
outbound proxy's route and backend metrics layers, and 2: remove status
code measurement from the NewRecordResponse middleware.

it's worth stating explicitly that this maintains the existing behavior of the
outbound proxy, and that (1) and (2) must be performed at the same time to
maintain parity.

to demonstrate that parity is maintained, let's compare metrics from this
branch against a snapshot of metrics exported in main.

🟰 comparing the metrics

metrics were scraped from the proxy, using a small traffic generation
deployment that runs curl against a container running http-echo.

a snapshot of the route and backend status/duration counters on main:

# HELP outbound_http_route_request_duration_seconds The time between request initialization and response completion.
# TYPE outbound_http_route_request_duration_seconds histogram
# UNIT outbound_http_route_request_duration_seconds seconds
outbound_http_route_request_duration_seconds_sum{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 0.5594713199999999
outbound_http_route_request_duration_seconds_count{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 284
outbound_http_route_request_duration_seconds_bucket{le="0.05",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 284
outbound_http_route_request_duration_seconds_bucket{le="0.5",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 284
outbound_http_route_request_duration_seconds_bucket{le="1.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 284
outbound_http_route_request_duration_seconds_bucket{le="10.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 284
outbound_http_route_request_duration_seconds_bucket{le="+Inf",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 284
# HELP outbound_http_route_request_statuses Completed request-response streams.
# TYPE outbound_http_route_request_statuses counter
outbound_http_route_request_statuses_total{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname="",http_status="200",error=""} 284
# HELP outbound_http_route_backend_response_duration_seconds The time between request completion and response completion.
# TYPE outbound_http_route_backend_response_duration_seconds histogram
# UNIT outbound_http_route_backend_response_duration_seconds seconds
outbound_http_route_backend_response_duration_seconds_sum{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 0.4626854930000003
outbound_http_route_backend_response_duration_seconds_count{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 284
outbound_http_route_backend_response_duration_seconds_bucket{le="0.025",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 284
outbound_http_route_backend_response_duration_seconds_bucket{le="0.05",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 284
outbound_http_route_backend_response_duration_seconds_bucket{le="0.1",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 284
outbound_http_route_backend_response_duration_seconds_bucket{le="0.25",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 284
outbound_http_route_backend_response_duration_seconds_bucket{le="0.5",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 284
outbound_http_route_backend_response_duration_seconds_bucket{le="1.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 284
outbound_http_route_backend_response_duration_seconds_bucket{le="10.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 284
outbound_http_route_backend_response_duration_seconds_bucket{le="+Inf",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 284
# HELP outbound_http_route_backend_response_statuses Completed responses.
# TYPE outbound_http_route_backend_response_statuses counter
outbound_http_route_backend_response_statuses_total{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name="",http_status="200",error=""} 284

this was repeated after applying config.linkerd.io/proxy-version to use a
proxy with these patches applied.

a snapshot of the route and backend status/duration counters with these
changes:

# HELP outbound_http_route_request_duration_seconds The time between request initialization and response completion.
# TYPE outbound_http_route_request_duration_seconds histogram
# UNIT outbound_http_route_request_duration_seconds seconds
outbound_http_route_request_duration_seconds_sum{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 0.2557158190000001
outbound_http_route_request_duration_seconds_count{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 128
outbound_http_route_request_duration_seconds_bucket{le="0.05",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 128
outbound_http_route_request_duration_seconds_bucket{le="0.5",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 128
outbound_http_route_request_duration_seconds_bucket{le="1.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 128
outbound_http_route_request_duration_seconds_bucket{le="10.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 128
outbound_http_route_request_duration_seconds_bucket{le="+Inf",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 128
# HELP outbound_http_route_request_statuses Completed request-response streams.
# TYPE outbound_http_route_request_statuses counter
outbound_http_route_request_statuses_total{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname="",http_status="200",error=""} 128
# HELP outbound_http_route_backend_response_duration_seconds The time between request completion and response completion.
# TYPE outbound_http_route_backend_response_duration_seconds histogram
# UNIT outbound_http_route_backend_response_duration_seconds seconds
outbound_http_route_backend_response_duration_seconds_sum{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 0.209469089
outbound_http_route_backend_response_duration_seconds_count{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 128
outbound_http_route_backend_response_duration_seconds_bucket{le="0.025",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 128
outbound_http_route_backend_response_duration_seconds_bucket{le="0.05",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 128
outbound_http_route_backend_response_duration_seconds_bucket{le="0.1",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 128
outbound_http_route_backend_response_duration_seconds_bucket{le="0.25",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 128
outbound_http_route_backend_response_duration_seconds_bucket{le="0.5",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 128
outbound_http_route_backend_response_duration_seconds_bucket{le="1.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 128
outbound_http_route_backend_response_duration_seconds_bucket{le="10.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 128
outbound_http_route_backend_response_duration_seconds_bucket{le="+Inf",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 128
# HELP outbound_http_route_backend_response_statuses Completed responses.
# TYPE outbound_http_route_backend_response_statuses counter
outbound_http_route_backend_response_statuses_total{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name="",http_status="200",error=""} 128

because there are a large number of metrics and labels, a character-level diff
of the two looked like so. as we'd hope, the only differences observed were
values of particular time series. in other words, the same traffic yielded the
same number of time series with the same labels.

diff --git a/recorded.txt b/recorded.txt
index 41d4c53..5bf5c13 100644
--- a/recorded.txt
+++ b/recorded.txt
@@ -1,29 +1,29 @@
# HELP outbound_http_route_request_duration_seconds The time between request initialization and response completion.
# TYPE outbound_http_route_request_duration_seconds histogram
# UNIT outbound_http_route_request_duration_seconds seconds
outbound_http_route_request_duration_seconds_sum{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} 0.{+2+}55[-94-]71[-3-]{+58+}19[-9999999-]{+0000001+}
outbound_http_route_request_duration_seconds_count{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} {+1+}28[-4-]
outbound_http_route_request_duration_seconds_bucket{le="0.05",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} {+1+}28[-4-]
outbound_http_route_request_duration_seconds_bucket{le="0.5",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} {+1+}28[-4-]
outbound_http_route_request_duration_seconds_bucket{le="1.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} {+1+}28[-4-]
outbound_http_route_request_duration_seconds_bucket{le="10.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} {+1+}28[-4-]
outbound_http_route_request_duration_seconds_bucket{le="+Inf",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname=""} {+1+}28[-4-]
# HELP outbound_http_route_request_statuses Completed request-response streams.
# TYPE outbound_http_route_request_statuses counter
outbound_http_route_request_statuses_total{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",hostname="",http_status="200",error=""} {+1+}28[-4-]
# HELP outbound_http_route_backend_response_duration_seconds The time between request completion and response completion.
# TYPE outbound_http_route_backend_response_duration_seconds histogram
# UNIT outbound_http_route_backend_response_duration_seconds seconds
outbound_http_route_backend_response_duration_seconds_sum{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} 0.[-46-]2[-685-]{+09+}4{+6+}9[-30-]0[-00003-]{+89+}
outbound_http_route_backend_response_duration_seconds_count{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} {+1+}28[-4-]
outbound_http_route_backend_response_duration_seconds_bucket{le="0.025",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} {+1+}28[-4-]
outbound_http_route_backend_response_duration_seconds_bucket{le="0.05",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} {+1+}28[-4-]
outbound_http_route_backend_response_duration_seconds_bucket{le="0.1",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} {+1+}28[-4-]
outbound_http_route_backend_response_duration_seconds_bucket{le="0.25",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} {+1+}28[-4-]
outbound_http_route_backend_response_duration_seconds_bucket{le="0.5",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} {+1+}28[-4-]
outbound_http_route_backend_response_duration_seconds_bucket{le="1.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} {+1+}28[-4-]
outbound_http_route_backend_response_duration_seconds_bucket{le="10.0",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} {+1+}28[-4-]
outbound_http_route_backend_response_duration_seconds_bucket{le="+Inf",parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name=""} {+1+}28[-4-]
# HELP outbound_http_route_backend_response_statuses Completed responses.
# TYPE outbound_http_route_backend_response_statuses counter
outbound_http_route_backend_response_statuses_total{parent_group="core",parent_kind="Service",parent_namespace="simple-app",parent_name="simple-app-v1",parent_port="80",parent_section_name="",route_group="",route_kind="default",route_namespace="",route_name="http",backend_group="core",backend_kind="Service",backend_namespace="simple-app",backend_name="simple-app-v1",backend_port="80",backend_section_name="",http_status="200",error=""} {+1+}28[-4-]

---

• feat(app/outbound): add status counters to route metrics
  Signed-off-by: katelyn martin kate@buoyant.io

• feat(app/outbound): add status counters to backend metrics
  Signed-off-by: katelyn martin kate@buoyant.io

• feat(app/outbound): add route status counting middleware
  Signed-off-by: katelyn martin kate@buoyant.io

• feat(app/outbound): add backend status counting middleware
  Signed-off-by: katelyn martin kate@buoyant.io

• refactor(app/outbound): remove status counter from duration middleware
  Signed-off-by: katelyn martin kate@buoyant.io

[cratelyn]

rebased on main now that #4298 and #4299 have been merged.