docs: link client call in builder

[dbolduc]

Currently these things are unlinked: https://docs.rs/google-cloud-kms-v1/latest/google_cloud_kms_v1/builders/autokey/index.html

While we're here, avoid "a" vs. "an" weirdness.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.94%. Comparing base (e47ccd7) to head (447756c).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1678   +/-   ##
=======================================
  Coverage   95.94%   95.94%           
=======================================
  Files          47       47           
  Lines        1850     1850           
=======================================
  Hits         1775     1775           
  Misses         75       75           

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