Make pystencils and lbmpy submodules of waLBerla
At the moment pystencils and lbmpy are installed from pypi using the latest version. Thus larger changes in pystencils or lbmpy lead to a failure in all pipelines as long as waLBerla is not adapted to the changes.
A solution to this problem is to make pystencils and lbmpy submodules of waLBerla. Then an MR can be created updating to the latest version. Additionally, users can install pystencils and lbmpy directly from the waLBerla submodule which ensures that they have a version which is well tested with waLBerla