Add links to fem data

[winfried-ripken]

Description

Integrate data links to catalog for paper "Learning the Solution Operator of Boundary Value Problems using Graph Neural Networks"

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring including code style reformatting
• Other (please describe):

Checklist:

• I have read the contributing guideline doc (external contributors only)
• Lint and unit tests pass locally with my changes
• I have kept the PR small so that it can be easily reviewed
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• All dependency changes have been reflected in the pip requirement files.

[axkoenig]

looks good, except 1 comment. if you want you could also add Merantix Momentum or the paper title in the metadata of each source, but this is not a must (maybe we can think of some policy here)

[axkoenig]

delete

[winfried-ripken]

thanks for the quick review! Nice idea about the metadata, will do 👍