Add testing with PyTest and GitHub Actions workflow

[smokestacklightnin]

This PR adds config to use pytest to run existing tests. A GitHub Actions workflow is also included. Additionally, there is a composite setup-env action that can be used in other workflows that sets up and installs the specified package in the current environment. Separate configs and CI workflow runs are used for the root package, fairness-indicators, and tensorboard_plugin.

There is one xfailed test that will need to be addressed in future work.

[smokestacklightnin]

Can whoever has the correct access please add a reviewer (or more than one) and give me the privileges to add reviewers?

In the meantime, does @peytondmurray have any comments, questions, or suggestions?