Fix issue when creating `JointGridContainer` with `SwitchInput`

[staudtMarius]

When building a JointGridContainer with SwitchInputs at the hv side of a transformer, an exception is trown. We should therefore discuss on how to fix this issue.

[danielfeismann]

Seems to be linked with #1310

[danielfeismann]

As per discussion:
Adapt definition of SubGridContainer to have the subgrid number aligned with the galavic separation of each grid. Documentation needs some adaption. Most probably some parts in the code as well (search method for linked switches, etc...)