Integrate flake8 with GitHub Actions

[dixonwhitmire]

Integrate the Flake 8 library, as documented in the README in the GitHub actions continuous integration workflow. The action should "fail" if flake8 finds issues.

[dixonwhitmire]

@klwhaley @LisaWellman @cragun47 - I would recommend working locally with autopep8 and flake8 for a bit before we enforce a linting rule on the repository. That will allow us to fine tune the rule's we're using.