docs: Generate samples for simple RPCs

[amanda-tarafa]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.80%. Comparing base (76070ae) to head (0f965e3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4095      +/-   ##
==========================================
+ Coverage   94.78%   94.80%   +0.01%     
==========================================
  Files         182      182              
  Lines        6885     6885              
==========================================
+ Hits         6526     6527       +1     
+ Misses        359      358       -1     

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[amanda-tarafa]

Test failures are unrelated to this PR, and seem to be in some Storage tests, for example:

[dbolduc]

nit: I think we would prefer to use the re-exported Result over gax::Result:

# use google_cloud_secretmanager_v1::Result;
async fn sample(...) -> Result<()> { ... }