Fixes for Github Actions sink

[mbarrien]

This PR adds fixes based on a previous github actions rotator prototype, and reduces the dependencies in go.mod.

• Adds response code checks and prints human-friendly errors if response codes aren't as expected
• Fixes an issue where it would always return an error even on success
• Adds YAML marshalling
• Removes explicitly passing in rand.Reader; relies on underlying box.SealAnonymous to provide the crypto.

[mahmoudian1]

Codecov Report

Merging #45 into master will decrease coverage by 0.73%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #45      +/-   ##
==========================================
- Coverage   24.10%   23.37%   -0.74%     
==========================================
  Files          15       15              
  Lines         477      492      +15     
==========================================
  Hits          115      115              
- Misses        351      366      +15     
  Partials       11       11              

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