[MakisH]

This PR migrates pulsating-flow-over-flexible-flap-3d-case1 to the tutorials and adds it to the system tests.

The reasons I selected this case are:

• It is relevant: The case comes from a benchmark, and we simulated the same in the OpenFOAM-preCICE paper,
• The perpendicular-flap case that would be simpler would be confusing, as it would need a different precice-config.xml (the current one assumes 2D, the one for OpenRadioss would need 3D, unless the adapter is modified to support 2D simulations).
• The blast cases were meant to be preliminary studies and more application-specific / demanding. They could, however, serve as examples/test cases for rhoPimpleFoam.

In the process, I have made some changes:

• The tutorial is now called perpendicular-flap-3d, instead of the original name pulsating-flow-over-flexible-flap-3d for two reasons: (a) to better relate with the current perpendicular-flap tutorial, (b) to keep the name shorter. There is another perpendicular-flap-3d case in the original repository, but that is pseudo-2d, since the flap takes the complete third dimension and it only has a few cells per it.
• I added the setup-openradioss.sh script under tools/. I removed the shopt -s expand_aliases.
• I commented-out the toVTK at the end of the run.sh, to make the anim_to_vtk tool optional, as it is an additional dependency.
• I removed the hard-coded export:vtu tags. They are not used, and the system tests add an exporter anyway.
• I rewrote most of the README.md in the style of a tutorial, and I added images from my local run (with 4 MPI ranks).

Note that this case is quite heavy. With 4 MPI ranks for the fluid, the case took 4h30m on my laptop to complete (max time: 30s). This PR sets the default to 8 MPI ranks and gives related hints in the documentation.

Also note that, while OpenRadioss as we know it does not exist anymore, I kept the name for historical continuity, and since the case was originally developed for OpenRadioss. The system tests use OpenCourant (the main open-source/community fork at the moment), and the README will point to it as well.

The system tests fail at the comparison step, even if I pin the OpenCourant version. This confuses me, but it is already good to know that the tutorial works. Note that the documentation recommends running OpenFOAM in parallel to save time, but the tests run OpenFOAM in serial (no particular reason; I just only realized now; I might change this when I look deeper into the numerical differences).

Checklist

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

@carme-hp could you please have an overview look and try to run the case?

@elisa-santoro FYI. Please let me know if you spot anything wrong.

I would like to get this merged soon, to have it in the upcoming tutorials release (and @elisa-santoro in the next distribution release). It's already been a while that this project has been completed.