Add CO2 network

[fneum]

Regionally resolve CO2 storage and add pipeline transport network because geological storage potential, CO2 utilisation sites and CO2 capture sites may be separated.

Simplifications

• Ignore retrofitting of the natural gas network as required pressures are too high (80-160 bar vs <80 bar).
• Ignore other modes of CO2 transport (ship, road, rail).
• Assume bidirectional pipes (like for H2 network currently).

Remaining TODOs

• extra_functionality for allowed sequestration potential
• add regionally resolved CO2 sequestration potentials (coordinate with @lisazeyen) -> Add rule building regional CO2 sequestration potentials pypsa-eur#585
• network topology from electricity network (see Biomass transport #73)
• additional cost if submarine based on underwater_fraction?
• "process emissions CC", "gas for industry CC", and "solid biomass for industry CC" should be nodally resolved. As minimal version, a link is added to each local CO2 store (if nodally resolved) that allows the copperplated carbon capture to be distributed freely to local CO2 stores.

[lisazeyen]

@fneum Looks great! I think only the color for CO2 pipeline was missing. Feel free to change it to another color. We can add the CO2 sequestration potentials in a separate PR or would you prefer to add it directly on this branch?

[fneum]

Thanks for having a look and finding the missing colour. I would add the regionally resolved sequestration potentials in a separate PR.