Fix solar slope and add wind correction factor for wake effects

[pz-max]

Changes proposed in this Pull Request

Solar potential were out of order. The current solar profiles are generated for north Europe (slope facing southwards).
The proposed config adjustments are a bug fix that gives more realistic solar potentials (slope=0). Future work should generate locational dependent slope factors.

Additionally, a correction factor was applied as in PyPSA-Eur to represent wake effects.

Checklist

• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Changes in configuration options are added in all of config.default.yaml, config.tutorial.yaml, and test/config.test1.yaml.
• A note for the release notes doc/release_notes.rst is amended in the format of previous release notes, including reference to the requested PR.

[pz-max]

@davide-f solar potential was quite underestimated. Merging this after the check.

[euronion]

Any particular reason to use fixed slope=0 and not latitude_optimal for pv?

[pz-max]

Awesome! It was just a quick fix. Didn't know it exist. Is this something which could change in PyPSA-EUR too?

[euronion]

You'd have to ask @coroa , it was initially latitude_optimal and later changed to fixed slope and orientation: PyPSA/pypsa-eur@b4dcbbb back in 2018. Maybe he remembers why it was changed in PyPSA-EUR . And maybe the same reason also applies here for Africa?