delivery: Re-write Unit Test config in GitHub Actions

[dinagraves]

Action

Re-write the (current unit test CI implementation) as a GitHub Action to improve visibility of test outcomes to all project contributors.

Background

In #94, we merged a unit test pipeline implemented in Cloud Build. In that PR, we discussed how to use GitHub Actions vs. Cloud Build.

[engelke]

I favor doing this, as it seems this would make test failure logs visible to committers.