Run notebooks in petsc jupyter image.

mention plane strain in smalldef verification example (tiny change)

It is customary in geomechanics to use plane strain assumptions for modeling mechanics in 2D.
However, users with another background than geosciences should be able find somewhere in the documentation (search function) which assumptions are made.
Topically this belongs to mechanics, so the best place for this hint seems the first benchmark example of the small deformation process, which is the verification.

See merge request ogs/ogs!3873

Allow utils build on PETSc config

See merge request ogs/ogs!3874

[BHE/docu] update 3 BHE array benchmark documentation

See merge request ogs/ogs!3872

[BHE/docu] lauguege rephrase according to the comment

[GeoLib] Cleanup/Modernize GeoLib related functionality.

See merge request ogs/ogs!3869

[GMSH2OGS] Enabled to convert more  high order elements to vtu

See merge request ogs/ogs!3809

[PL/TH2M] Extend Jacobian with Laplacian's derivatives.

See merge request ogs/ogs!3839

Disable too low order shapefunctions

See merge request ogs/ogs!3846

Commented for now because not tested.

[GeoLib] Add more unit tests for Polyline and  fix bugs detected by the tests.

See merge request ogs/ogs!3868