Adjust update_heat_timeseries_germany() for other years on scenario path

[ulfmueller]

Use the existing eGon code for the eGon100RE scenario but taking a scenario year specific yearly target value for DE. Possibly use p-e input data for the national yearly consumption.

[ClaraBuettner]

Im Bereich der Fernwärme wird in den Szenarien A und B von einer Steigerung des Wärmebedarfs von heute 125 TWh
auf 162 TWh im Jahr 2037 und 150 TWh im Jahr 2045 ausgegangen

(Seite 41 NEP 2023 https://www.netzentwicklungsplan.de/sites/default/files/2023-07/NEP_2037_2045_V2023_2_Entwurf_Teil1_1.pdf)

[ClaraBuettner]

Using the previous approach from eGon times seems to be not better than using the pypsa-eur data without any adjustments. It might make sense to scale to the demands that are closer to the assumptions from the NEP (study from Agora Energiewende), but that requires more changes.
So we agreed on not scaling the data at all. I will implement this soon.
If the results from pypsa-eur are far away from the NEP scenarios, we can still implement a scaling.