Merge into Cadabra repo / make it the official Docker container

[kpeeters]

I would be happy to merge this into the Cadabra repo to make it the official container distribution. That would also make it easier to update it automatically when a new version is released, and I am happy to upload it as an official Docker image for x86_64 and arm64.

I think there are various improvements you can make to reduce the size, e.g. dropping gtk libraries and so on (which you do not need if you only want the Jupyter kernel).

There are various unofficial cadabra2 docker files floating around on dockerhub, and it would be good for newcomers to streamline that a bit.

[fjebaker]

Hi @kpeeters sounds very good! Let's do it!

What's the best way to approach this? Should I open a PR on the Cadabra repo with the Dockerfile and then we can iterate in the PR branch to get the size down for the Jupyter version? Or would you prefer to work in this repo until it's ready?

[kpeeters]

I have already started adding this to the devel branch of the cadabra2 repo. It's in the docker folder. There is still something not quite right with paths on that one, but I am behind a very slow internet connection at the moment so testing/fixing is a bit of a pain.

I have also added github actions to build the docker image on amd64 and aarch64, in .github/workflow/. This works and builds new images automatically on every push, but it needs some tagging of the resulting images with the cadabra version number before I can enable uploading to dockerhub.

If you want to propose changes, please open a PR against this devel branch.