Adjust reading of joint grid container to be able to parse hierarchic grid structures.

[t-ober]

Depends on: ie3-institute/PowerSystemDataModel#769

The Gridprovider.gridFromConfig method currently does not consider the isHierarchic parameters but just assumes a flat directory hierarchy. This should be changed, after the corresponding option is available in the PSDM

[jo-bao]

Solved with PSDM 4.0