add Biomethanation

[BertoGBG]

Closes # (if applicable).

Changes proposed in this Pull Request

added biomethantion technology (biological methantion of CO2 with electrolytic H2). The technology is part of the DEA catalogue and it was added via compile_cost_assumptions.py

Checklist

• [ Y] Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• [ Y] Data source for new technologies is clearly stated.
• Newly introduced dependencies are added to environment.yaml (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• [Y ] I consent to the release of this PR's code under the GPLv3 license.

[fneum]

Can we make the renames more consistent with the most commonly used names?

hydrogen-input
co2-input
electricity-input etc.

[BertoGBG]

I have updated the names to the most commonly used names (eg. methane-output insect of Methane Output).
for the final DF and csv file.
Note that the index names set in biomethanation_dea (like "El-Input", "H-Output") (the lines you mentioned) are only used as search keys by str.contains() in the filtering at lines 2155–2204 and 2312–2340. They never appear in the final CSV.