Add official docker images

[pljones]

What is the current behaviour and why should it be changed?

Currently, anyone wanting to deploy Jamulus in a docker container has to come up with their own solution.

Describe possible approaches

We could keep things as they are but it means the divergent projects that use docker each have to re-invent the wheel.

Ideally, there would be official images produced for release builds (not on every PR) and the artifacts published to appropriate docker image repositories.

Has this feature been discussed and generally agreed?

Briefly here:
#3692 (comment)

[ann0see]

While technically it's nice to have, I'd rather prefer to focus on good deb and binary builds and leave docker, flatpak, snap, ... to the wider community. We can link it on jamulus.io but I'd rather not make those official. It's too much that can break and if someone else has good knowledge on packaging/deployment they should do it on their repo.