Clustering of H2_grid buses relies on H2_feedin links

[AmeliaNadal]

The H2_grid buses have the same localisation than the CH4 buses and their clustering is using the one of the CH4 grid. Therefore, the H2_feedin links (connecting each CH4 bus to its corresponding H2_grid bus) are used to establish the correspondence. For cases where H2_feedin is not present in the system or for the eGon100RE scenario, this should be changed. An easy option would be to replace the "H2_feedin" links by "H2_to_CH4" links but there is maybe a more elegant way to do it.

See: https://github.com/openego/eTraGo/commit/1a8606971df05c968ac339102270691a44f6f3d5

[pieterhexen]

WIP on https://github.com/openego/eTraGo/tree/features/update_clustering

TODO:

• [x] Change H2_feedin dependency in gas clustering to sql-table based ch4_h2_mapping
• [x] Add csv import and export for self.ch4_h2_mapping
• [x] Test

[pieterhexen]

In oder to make the gas clustering work for the eGon100RE scenario the following lines need to be adapted to also account for H2_retrofit and H2_gridextension links: https://github.com/openego/eTraGo/blob/79a4fda44aeece79c8306dec073f69e780f6c4cc/etrago/cluster/gas.py#L764-L773

Will be implemeted and tested when AC clustering is working for eGon100RE

[pieterhexen]

Done in https://github.com/openego/eTraGo/pull/595