Compatibility of data processing for Ukraine

[Irieo]

Changes proposed in this Pull Request

Add_electricity.py from master branch breaks when "UA" is in the list of countries. This takes place in attach_load() function with KeyError: "['3118'] not in index". This is likely introduced by the recent update of polygon simplification defaults, see #1100

What's happening: UA and MD have special keys of distributing load across regions (since the countries are not part of the NUTS system).
the ditribution keys were pre-computed here and stored as csv here
Data in GDP_PPP_30arcsec_v3_mapped_default.csv does not contain bus 3118 , since it was likely filtered out with poligon simplification. See illustrations below.

Another, more general problem: distribution keys should generally be part of the data workflow. With the incoming change of GridKit extract to OSM data (#1079), substation IDs will change and will be subject to frequent updates.

Suggestion

• introduce a new rule and script for downloading raw GDP and PPP data for UA (conditional to UA in country list)
• fix distribution key
• map GDP_PPP to UA onshore shapes within workflow (PENDING)

Checklist

• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in all of config.default.yaml.
• Changes in configuration options are also documented in doc/configtables/*.csv.
• A release note doc/release_notes.rst is added.