Adding github workflow

[iam-dev]

Add a github workflow for automated testing and slither test
see also: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/.github/workflows/test.yml
https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/.github/workflows/slither.yml

[0xCourtney]

I was just thinking about this as well. Any updates here? Preferences on workflows? We use one for automated tests, linter checks, and code coverage on Knox Finance. Adding an action for slither could be very useful.

[ItsNickBarry]

This is worth considering, but not something I want to rush into. Two concerns:

1. Bot spam is annoying.
2. GitHub workflow ties the project specifically to GitHub. Migration to any other platform would therefore be more disruptive.