[GeoMechanicsApplication] Re-enable the C++ settlement test

[avdg81]

We have a C++ GTest which runs the settlement workflow as provided to the settlement team (i.e. the C++ API). However, due to the lack of C++ tools to compare with tolerances this test is disabled.

This issue is there to re-enable the 4-staged settlement test through the C++ API.

Background
To do this, we can create the C++ API object in python, run the stages there and make use of our tools to compare results at certain nodes with a tolerance.

For experimentation done on this, see test-settlement-cpp-test