POC: WIP: Add gallery example for 3-D bar plot

examples/gallery/3d_plots/3d_bar.py

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+"""
+3-D bar plot
+============
+Based on GMT EXAMPLE 08
+https://docs.generic-mapping-tools.org/6.6/gallery/ex08.html
+Convert grid to table: :func:`pygmt.grd2xyz`
+Plot in 3-D via bars: meth:`pygmt.Figure.plot3d`
+"""
+
+# %%
+import pygmt
+
+region = [141, 147, 36, 43]
+grd2tab = pygmt.grd2xyz("@earth_relief_10m", region=region)
+grd2tab["color"] = grd2tab["z"]
+z_min = grd2tab["z"].min() - 50
+z_max = grd2tab["z"].max() + 50
+
+fig = pygmt.Figure()
+
+fig.basemap(
+    region=[*region, z_min, z_max],
+    projection="M10c",
+    zsize="10c",
+    perspective=[195, 30],
+    frame=["WSneZ", "xaf", "yag", "za1000f500+lElevation / m"],
+)
+
+pygmt.makecpt(cmap="SCM/oleron", series=[z_min, z_max])
+fig.plot3d(
+    data=grd2tab,
+    cmap=True,
+    pen="0.01p,gray30",
+    style=f"o0.34c+b{z_min}",  # bars o, base +b
+    perspective=True,
+)
+fig.colorbar(frame="xa1000f500+lElevation / m", position="jTR+o1.8c+v+w7c+ml")
+
+fig.show()