Add Github Actions for Pull Requests

[nateprewitt]

This PR will add some basic Github Actions for our pull requests. Three workflows run that will:

1. Run our functional and unit tests on Python 3.{6-8}
2. Lint the Pull Request and existing code base with black and flake8
3. Run type checking with mypy
   • This currently ignores errors from awscrt and doesn't enforce --strict. That will be handled in a future CR.

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (develop@b099801). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff             @@
##             develop       #2   +/-   ##
==========================================
  Coverage           ?   88.87%           
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  Files              ?       33           
  Lines              ?     1861           
  Branches           ?        0           
==========================================
  Hits               ?     1654           
  Misses             ?      207           
  Partials           ?        0           

Flag	Coverage Δ
#unittests	88.87% <0.00%> (?)

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[joguSD]

Is the linting and type checking running multiple times? Curious why all of the actions show up 3x.

[nateprewitt]

Which UI were you looking at? It should only be running twice, once for push and once for the pull request. The "Actions" tab at the top lumped in one additional run from a separate branch for some reason. The last three are for actions_cov instead of actions.