Add Shunt controller & more descriptive validation in PF2pp validate

[pawellytaev]

Warning, this PR has station controller merged into it. Merge this only after PR #2228 is merged

This PR contains:

• Discrete shunt controller for local voltage regulation with shunts
• more descriptive PF2pp diffs --> now as DataFrame with columns diff, pandapower results & PowerFactory results. Currently not implemented for all elements, this will be done in a separate PR

[codecov]

Codecov Report

Attention: Patch coverage is 64.89362% with 66 lines in your changes missing coverage. Please review.

Project coverage is 76.00%. Comparing base (be0f2cf) to head (6e4d088).
Report is 25 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ower/converter/powerfactory/pp_import_functions.py	0.00%	31 Missing ⚠️
pandapower/converter/powerfactory/validate.py	75.86%	21 Missing ⚠️
pandapower/control/controller/shunt_control.py	79.10%	14 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2380      +/-   ##
===========================================
- Coverage    76.04%   76.00%   -0.04%     
===========================================
  Files          281      282       +1     
  Lines        32798    32943     +145     
===========================================
+ Hits         24940    25038      +98     
- Misses        7858     7905      +47     

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