Run unit tests in Github Actions

[krisgesling]

Description:
Adds automated testing for any new PR via Github Actions.

Intentionally commented out flake8 checks at the moment as these will fail on the current codebase.

How to test:
See automated checks below.

CLA

• Yes

[forslund]

Looks good and is working, did comment on the flake-8 test which can be partially activated to check for some common mistakes.

[forslund]

Discussing abit with @krisgesling yesterday and we've now updated to use test-requirements.txt to install pytest and flake8.

The run_tests.py script is removed for the time being since it's not used anymore. testing instructions have been added to the readme for now. A new script should probably be created to allow running the flake8 and pytest...

[forslund]

Since the flake command-line is non-trivial I pulled it out into a run_tests.sh script as you suggested @clusterfudge, readme has been updated with this information.

[clusterfudge]

lgtm!

Thanks @forslund for pulling this across the line. Please open an issue for us to address/document&ignore the lint errors we're excluding with --select=E9,F63,F7,F82

[forslund]

Will write up an issue during the day.