Port INI files in experiments/ to YAML

Description

The input files in two subfolders of experiments/ are still given in the now obsolete INI file format. They have to be ported to YAML to be used in the current version of dune-structures.

These INI files also provide information for the GMSH generation algorithm, which has not been tested so far.

Proposal

• Port INI files to YAML
• Add execution of GMSH generator and other experiments to testing pipeline.
  • *(if needed:) Adapt GMSH generator and/or input files to work properly.