Add a github action to build and test project

[adrianparsons]

This adds a github action to run when PRs are opened against master.

Basically, the action:

1. Spins up an Ubuntu environment
2. Creates a postgres "service"
3. Starts the mysql server (installed by default on Ubuntu)
4. Configures mysql and postgres for tests
5. Installs nmig dependencies, builds the project, and runs tests

See my fork for examples of test runs.

This PR adds a github action file, but actions have to be enabled in the project to actually run.

I'd like to eventually expand this to include tests for the Docker workflow.