Move CI to Github actions

[grahamgilbert]

The current CI doesn't work well with PRs and GH actions handles this just fine, so that's reason enough to move really. It looks like we can use https://github.com/marketplace/actions/build-and-push-docker-images for building, I just need to work out if we can trigger the saml build (or if we just do it on this repo).

[ChefAustin]

One option for triggering cross-repo GHA Workflow => https://medium.com/hostspaceng/triggering-workflows-in-another-repository-with-github-actions-4f581f8e0ceb