chore: fix i18n imports and usage

[edoardo]

Key features

1. use the same import for i18n everywhere
2. ensure i18n.t gets executed for all translatable strings

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Description

We had 2 ways of import i18n in the library.
I don't think we had problems due to this, but for consistency sake and to avoid possible issues, it's good to import everywhere from the same place.
Importing from locales/index.js ensures that the library translations are added and are available in the consumer apps.

Some strings did not show translated in consumer apps, the reason is likely marking i18n.t strings in static constants or objects, in that case the i18n.t function is not called at runtime.

[jenniferarnesen]

Kind of a weird sentence (I know this was already present): "Create a new to get started."

[HendrikThePendric]

I wonder if there is perhaps a better solution to this problem. The current solution has 2 downsides as I see it:

1. importing from the file locales/index.js is less ergonomic than importing from the package @dhis2/d2-i18n
2. The file locales/index.js actually does do quite a lot. If we import this file in a lot of places the calls to .addResources() will be happening often. I don't know if this is a problem, but doesn't seem desirable

I'm thinking the following:

1. To ensure we always "load the translations" for consumers of the lib, we can import the locales/index.js file from our own index file, since consuming apps should be importing from there exclusively (if this is not true, I think the current implementation in this PR is probably the best solution)
2. To avoid running the code in locales/index.js multiple times, we probably would have to do a dynamic import, i.e. something like this:
   1. Import the i18n singleton from @dhis2/d2-i18n
   2. check if our translations have been added (not sure how, but I think it may be possible)
   3. If not dynamically import the locales/index.js file
3. We could consider checking how this is done in @dhis2/ui