Fixing Errors in GB Hydropower Capacity of ~5GW

[LukasFrankenQ]

Change proposed in this Pull Request

There appear to be some inconsistencies between the data underlying ppl and other datasets of powerplants in GB. This datasheet gives an interesting example of this, and also shows how widespread the errors seem to be. It hints towards typos that could have set some capacities to 999 MW.

By manually checking the most problematic cases of this in Google Maps, I propose manual changes to ppl that accumulate to a reduction of ~5GW of hydropower capacity in Scotland and Wales.

I somewhat randomly added the value "ENTSOE" to the Source column, which appears to play a role in merging manual_corrections.csv. Please let me know if this needs adjustment.

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [X] Other

Checklist

• [X] I have added a note to release notes doc/release_notes.rst.
• [X] I have used pre-commit run --all to lint/format/check my contribution
• [X] I have documented the effects of my code changes in the documentation doc/.
• [X] I have adjusted the docstrings in the code appropriately.