Nearly all the github actions we rely on have increased their major
version, at least to update the Node.js version they run on, since the
previous one is being deprecated and will eventually become unsupported.
So this patch updates all the versions of the github actions we use.
We're running against the usage limits in Gitlab CI (500), and Github
Actions should have more (2000).
So this patch replaces Gitlab CI with Github actions for running
integration tests, and build and push Docker images (to Dockerhub and
Gitlab registry).
We'll see how the usage levels are in a few months.
