feat: API key authentication

[dbolduc]

Part of the work for #14759

Introduce a dedicated API for authenticating with API keys.

Update the sample because it doubles as an integration test.

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This change is 

[scotthart]

Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @dbolduc)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.27%. Comparing base (db36db3) to head (2b6d26e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14779   +/-   ##
=======================================
  Coverage   93.27%   93.27%           
=======================================
  Files        2317     2317           
  Lines      208162   208171    +9     
=======================================
+ Hits       194157   194174   +17     
+ Misses      14005    13997    -8     

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