More Dockerfiles

[dreibh]

This pull request adds a small script to write Dockerfiles for a set of Distribution/Architecture combinations, where DockerHub provides docker images. Also, the resulting Dockerfiles are added, so that they can be used by Git Actions.

[uraimo]

Thanks for the script&dockerfiles!

@elijahr I was not sure if it makes sense to add at least a portion of these (unstable, latest) to the basic test but probably not, even one single test for every arch should be enough regardless of the OS. Individual issues can be fixed when reported. Feel free to merge if you don't have further comments.

[radimkohout]

This won't work.
The script will add non-functional configs (for example riscv64 has only experimental, sid, and unstable, see here: https://hub.docker.com/r/riscv64/debian/ ; but you're also generating stretch, jessie, buster, bullseye, and bookworm). I've already tried to do something like this, but I failed due to many non-existent versions for some platforms.