Add Github api client and wrapper functions for CI/CD api

[hdoupe]

• Adds Github API wrapper for repos, pull requests, actions, etc. I went with a custom implementation because other Github API clients do not implement the Actions endpoints yet (an issue to watch: GitHub Actions support PyGithub/PyGithub#1373). I also wanted something that would be simple and easy to work on instead of trying to extend an existing package with lots of inheritance that would be hard to debug.
• Adds a script with functions for starting a CI/CD job and checking its status. This will be used by the cluster API endpoints.

Resolves #437