PyWorkflow unit tests and GitHub Action file

[reelmatt]

This PR:

• adds unit tests for PyWorkflow package
• renames Postman files to make CLI execution easier
• creates a GitHub Actions file to automate tests on push to master and creating PRs

We had mentioned using Jenkins in our reports, but it looks like GitHub Actions will be much easier to implement. This is my first time using them, so the workflow script could probably use some work. In particular, a lot of the Python actions are grouped together in one 'job' because I was having trouble splitting them up.

This is also my first time writing tests (!) so they may need changes, but it seems like a good first step to me. They include a mix of some positive/negatives tests, just focusing on the Workflow class to start.

[reelmatt]

I've been testing the GitHub Action locally using act and using the environment mentioned in the 'Runner' section. Seems fine locally; failed when I create the PR due to a YAML syntax error (now fixed, but didn't re-run).

According to the pricing page it looks like public repos get unlimited minutes for actions, so shouldn't be a problem. I'll update the workflow to trigger on every push.