Use linopy formulation

[ClaraBuettner]

The new pypsa versions include optimizing with linopy (instead of pyomo).
This is already used in this branch: https://github.com/openego/eTraGo/tree/features/market-simulation-electrolysis-dispatch

The constraints used by default (CH4 and CHP) are already translated on that branch. This needs to be done for the other optional constraints as well.