[SUB] Update biogas and biomass dispatch in CBA

[measrainsey]

• Replaces [SUB] Use marginal costs for biomass and biogas generators/links in CBA #510
• Parent issue: [PARENT] Improvements rolling horizon #324

In the CBA workflow, the dispatch of biomass and biogas generators would be better represented similar to how Stores are represented: get the marginal price at the bus for which the generator is attached -> Add this as marginal cost to the generator

Tasks

• Extract marginal price for biomass and biogas generators
• Use the marginal prices as marginal costs of generators