Secret Manager Integration

[bbengfort]

This is the final step for a complete implementation of the v1 Whisper
app. Whisper is now no longer stateless but saves both secret context
metadata and the secret itself in Google Secret Manager. Most of the
logic of interacting with secrets has been moved out of the API and into
the Secret Manager codebase.

[codecov]

Codecov Report

Merging #6 (095c708) into main (d873e55) will decrease coverage by 12.62%.
The diff coverage is 0.72%.

❗ Current head 095c708 differs from pull request most recent head 60c7fb9. Consider uploading reports for the commit 60c7fb9 to get more accurate results

@@             Coverage Diff             @@
##             main       #6       +/-   ##
===========================================
- Coverage   32.69%   20.07%   -12.63%     
===========================================
  Files           8        8               
  Lines         364      563      +199     
===========================================
- Hits          119      113        -6     
- Misses        220      424      +204     
- Partials       25       26        +1     

Impacted Files	Coverage Δ
pkg/secrets.go	12.03% <0.00%> (-3.54%)	⬇️
pkg/vault.go	0.00% <0.00%> (ø)
pkg/version.go	25.00% <ø> (-12.50%)	⬇️
pkg/whisper.go	44.21% <25.00%> (-1.77%)	⬇️

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[rebeccabilbro]

Looks good! Nice to see some familiar bits and pieces from knock 🚪 🙂

I like the inclusion of the metadata versioning, and I think it's really neat that we've figured out how to do this with no database, at least to start!