CI: Build and store a Docker image

[MakisH]

This PR builds a Docker image with preCICE, OpenFOAM, and the current state of the OpenFOAM adapter from the add-ci-docker branch, and pushes it to GHCR. (under construction, currently experimenting)

TODO list:

• I updated the documentation in docs/
• I added a changelog entry in changelog-entries/ (create directory if missing)

[BenjaminRodenberg]

I would like to review this PR as soon as it is done (just as a note). Especially, since I have my own similar side project here: https://github.com/precice/fenics-adapter/blob/develop/.github/workflows/build-docker.yml. We should try to synchronize these two before we roll the methodology out to all adapters etc.

[MakisH]

We now have a first minimal version of the system tests in the develop branch of the tutorials, which builds a Docker image of the OpenFOAM adapter on demand when triggered, given arguments regarding the OpenFOAM version etc.

To avoid publishing intermediate images, we want to rely on the GitHub Actions cache. Read more in precice/precice#1700.

We could still publish Docker images of the released versions of the adapter, to reduce the runtime of specific workflows.

[MakisH]

Closing in favor of the multi-stage Docker build approach discussed in precice/precice#1700

After a first prototype for that works, we should also remove the published test image from the GitHub Container Registry.

[MakisH]

Closing as the same goal is now achieved by precice/tutorials#364.
Deleting the old Docker image as well.