distribute electricity demand by JRC energy atlas

[fneum]

Closes #1810 .

Changes proposed in this Pull Request

Distributing country-level electricity demand time series to subnational model regions of EU countries now uses data from the JRC Energy Atlas.
This dataset provides electricity consumption on a 1 km by 1 km raster for the year, which is more accurate than the previous NUTS3-based distribution.

Another dataset is used for Great Britain from the Department for Energy Security and Net Zero.

Other non-EU countries still use NUTS3-based distribution keys from GDP and population.

New Dataset Visualization

Area-normalized demand (master versus feature)

Checklist

• [x] I tested my contribution locally and it works as intended.
• [x] Code and workflow changes are sufficiently documented.
• [x] Changed dependencies are added to envs/environment.yaml.
• [x] Changes in configuration options are added in config/config.default.yaml.
• [x] Changes in configuration options are documented in doc/configtables/*.csv.
• [x] Sources of newly added data are documented in doc/data_sources.rst.
• [x] A release note doc/release_notes.rst is added.

[coroa]

At first glance, i am very surprised how well the naive electricity demand downscaling by gdp/pop did in comparison to this detailed dataset.