[WIP] Add solid-mfem to flow-over-heated-plate

[j-signorelli]

This PR adds an MFEM implementation of preCICE for the flow-over-heated-plate tutorial.

Checklist

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md.
• If I changed requirements.txt files, I regenerated sibling requirements-reference.txt files with python3 .dev-tools/releasing/update-requirements-reference.py (pass a path to update only that directory, or --all to refresh everything).

For new tutorials or tutorial cases:

• I followed the tutorial folder structure
• I added/updated the tutorial README.md
• I added/updated the tutorial metadata.yaml
• I added tests in tests/tests.yaml
• I submitted a pull request to the website with:
  • An entry in _config.yaml
  • A sidebar entry
  • An entry in the tutorials overview

[MakisH]

@j-signorelli nice to see this draft!

Hint on the failing CI: we use pre-commit and this also checks and adjusts the formatting of some files. After you install it, do pre-commit install and pre-commit run -a to fix the files. Read more.

We can clearly improve the contributing guidelines here (tricky among multiple repositories). Any feedback is welcome.

[j-signorelli]

@MakisH gotcha, thank you!