Pending issues with NB and PowerGrids

[casella]

This ticket collects known issues involving the PowerGrids library and the NB.

• #10034. This is really important, specifically to solve initialization problems in power grid models
• #12237 (as I understand, the initialization problem is not overdetermined at all)
• #12543
• #12943
• #13003
• #13058
• #13076