[FEATURE] Automatic adjustment of transformer tap changer

[TonyXiang8787]

Feature

• Add control logic for transformer tap changer.
• In power flow calculation, add an option to change the tap changer of transformer automatically.

Considerations

• How to model tap changer controller? A separate class or inside transformer?
• How to implement it in the power flow solver?

[Jerry-Jinfeng-Guo]

For the tap changer, we implemented a ranking algorithm for transformers (with tap) in the following PRs:

• [STEP 1]
• Feature/Transformer ranking - Step 2-3 #545
• Feature/transformer ranking step 4 #558
• [UNIT TEST]