Mapping tester save case information in case dir

[fsimonis]

Currently, the mapping tester extracts information of different cases from the path to the case.
This is error-prone and tedious to use as a single case doesn't hold the information of its setup.

Instead, we should write a json or yaml describing the case setup in the case directory:

{
        "mapping": "nearest-projection",
        "constraint": "consistent",
        "mesh A": 0.01,
        "mesh B": 0.0001,
        "ranks A": 2,
        "ranks B": 4
}