[Experimental] Add CI GitHub Actions workflow

[rajadain]

Overview

Because of the absence of nested virtualization support on GitHub Actions, we cannot run Vagrant / Ansible / Packer tasks on the vanilla Linux runners. However, Vagrant is supported on macOS runners, which unfortunately are 10x more expensive than the Linux runners.

Furthermore, because of the ephemeral nature of GitHub Actions, we don't get any advantages of VM reuse, since they have to be provisioned from scratch every time. Thus, a Jenkins CI build which takes between 8-20 minutes, takes about an hour on GitHub Actions, because it is provisioning every VM from scratch every time, even though we are caching the Vagrant boxes and VMs.

Further Reading:

• https://github.com/jonashackt/vagrant-github-actions
• https://stackoverflow.com/questions/66261101/using-vagrant-on-github-actions-ideally-incl-virtualbox
• https://gopheradvent.com/calendar/2021/how-chezmoi-implements-cross-platform-ci/

Connects #3584

Demo

Some successful runs:

• https://github.com/WikiWatershed/model-my-watershed/actions/runs/3808688618/jobs/6479817695
• https://github.com/WikiWatershed/model-my-watershed/actions/runs/3808575851/jobs/6479272073
• https://github.com/WikiWatershed/model-my-watershed/actions/runs/3808291636/jobs/6478744345

Recommendation

Because of the high cost of operation and the architectural impedance of running persistence based workflows in an ephemeral environment, it would be best to consider using a custom external runner for this. That would allow us to take advantage of persisted states, keep the running costs low, and implement arbitrary workflows without the limitations faced above.

This PR should not be merged, but can be left open to serve as a reference implementation for the local runner attempt.