Improve Clustering with Focus Region

[KathiEsterl]

The clustering with a regional focus should be extended and refined in the following aspects:

• Review and potentially adapt the default parameterization.
• Reassess the argument options to improve the balance between user-friendliness and flexibility for use-case-specific configurations.
• Ensure compatibility with EHV clustering.
• (also with regard to EHV clusterning) Introduce a fallback mechanism:
  If no buses are located within the focus region (unlikely for AC grids, but possible for gas networks), the nearest node connected to the focus region should be used instead.
• Improve the “cluster within focus” option:
  Currently, clustering inside the focus region is only discouraged via very high weighting but not strictly prevented. Two possible approaches:

a) Replace the focus region with the original grid in that area and preserve voltage levels.
b) Strictly restrict clustering to nodes outside the focus region (as implemented, for example, in hybit (https://github.com/openego/eTraGo/tree/hybit) or opties-branch(https://github.com/openego/eTraGo/tree/features/opties)).

• Update documentation / read the docs

[KathiEsterl]

For the mentioned aspect of improving the "cluster within focus" option, we try version a) as part of this branch:

https://github.com/openego/eTraGo/tree/features/%23841-focus-clustering-keeping-voltage-levels