15 description of plate with hole in docs

[srosenbu]

Description of linear elastic plate with hole

Edit: Latex does not render correctly on github. The docs for this PR are built on https://nfdi4ingmodelvalidationplatform.readthedocs.io/en/15-description-of-plate-with-hole-in-docs/benchmarks/linear%20elasticity/plate-with-hole/

TODO:

• How do we link the jupyter notebooks with the postptocessing?
• What else do we want to remove from the docs?
• I also prepared a jupyter notebook with sympy calculations for the BCs. Should this be included too as a "tool-independent description"