Remove res from conventional ppls

[yerbol-akhmetov]

Changes proposed in this Pull Request

Here, I propose a slight modification of the code in add_electricity rule. Currently, in the attach_conventional_generators in add_electricity.py, non-conventional powerplants are also considered if extendable contains RES powerplants in config file. It does not currently create any problem, since those RES ppls added by attach_conventional_generators are rewritten by attach_wind_and_solar. In practice, only conventional powerplants need to be added by the attach_conventional_generators rule. I have faced this issue, when I tried further clustering (not only by carrier type, but also powerplant type (CHP and PP)).

Checklist

• I consent to the release of this PR's code under the AGPLv3 license and non-code contributions under CC0-1.0 and CC-BY-4.0.
• I tested my contribution locally and it seems to work fine.
• 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]

@yerbol-akhmetov good suggestion.

Do you think we can pass renewable_carriers here: attach_conventional_generators()
and instead of doing:
set(conventional_carriers) | (set(extendable_carriers["Generator"]) - {"solar", "onwind", "offwind-ac", "offwind-dc"})
do:
set(conventional_carriers) | (set(extendable_carriers["Generator"]) - set(renewable_carriers))

This is a bit more flexible in case new renewable carriers are added.

[pz-max]

Good suggestion. Can you check my comment and avoid the hardcoded parts?

[yerbol-akhmetov]

I have replaced hard-coded part with more general renewable_carriers.