This adds a new authentication mode, Direct Workload Identity
Federation. This new mode permits authenticating to Google Cloud
directly using the GitHub Actions OIDC token instead of proxying through
a Google Cloud Service Account.
* define common interfaces
* common base client
* refactor WIF to use interfaces and base client
* refactor main
* add build in CI
* add name for build step
* address comments
* fix import
* interface for credfile return
* regen dist