Clarify status of FEniCSx (adapter + tutorials)

[BenjaminRodenberg]

The status of the FEniCSx adapter and the corresponding tutorials is currently unclear. This is especially relevant for the upcoming distribution release. Some risks and open questions:

• FEniCSx latest release is version 0.7. I am not sure to which degree the API is considered stable and whether version 0.7 is compatible with the current state of the fenicsxadapter. I'm unsure which version of FEniCSx is required for the current state of the fenicsxadapter. The last working state should be related to the submission date of Philip Hildebrand's thesis.
• There is no release of the fenicsxadapter that we can consider stable. The current state is documented in https://github.com/precice/fenicsx-adapter/milestone/1.
• Compatibility of FEniCSx and FEniCS is unclear. Can we install both on the same system without conflicts? Related to Add FEniCSx to the vm vm#65. We definitely want to keep FEniCS at least for the upcoming distribution release. This is critical for my PhD thesis, but also reasonable looking at the number of tutorial cases, features, and experience we have for FEniCS compared to FEniCSx.

Our possibilities:

• Don't release anything related to FEniCSx in the upcoming distribution release. Does this mean we have to put FEniCSx tutorials onto a branch, open a PR, and remove them from develop?
• Fix issues and get to a minimal working version. Considering the points above this seems to be a major effort.
• "Documentation-based" approach. Don't remove anything from tutorials/develop, but clearly mark FEniCSx as under construction / experimental.

[uekerman]

And we would likely need a breaking FEniCSx adapter release for preCICE v3 compatibility.

[MakisH]

Summary of the discussion in the telco (a bit beyond the scope of this issue):

• Merging any tutorial means that we plan to maintain it.
• All tutorials included in the Distribution must support preCICE v3.
• Having a tutorial merged without a component being in the distribution is fine. In that case, we also don't install the respective code in the VM.
• Releases of components are independent of the distribution release. The latter only helps citing and integration in the VM.

Since this tutorial has not yet been merged in main, and @BenjaminRodenberg does not have time to port it before the release, let's remove it from develop and continue in a separate branch.

[IshaanDesai]

Closed via #488