We publish the LaTeX Docker image on Docker Hub, but Docker is nuking free team repos there, so users won't be able to pull the image from April onwards.

We should probably move the image hosting to GitHub's GHCR:

• https://docs.github.com/en/actions/publishing-packages/publishing-docker-images#publishing-images-to-github-packages
• https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry

While we're at it, we should also move the Dockerfile to this repo I think.