OPF enhancement - minimise maximum load / feed-in shedding

[birgits]

Is your feature request related to a problem? Please describe.
As the optimisation of flexibility dispatch is now, only the sum of the load and feed-in shedding is minimised. Therefore it is possible, that e.g. alot of load is shifted into one hour instead of being spread as much as possible over several time steps, which would lead to much higher grid expansion costs.

Describe the solution you'd like
TBD, but one option would be to include the minimisation of the maximum power that needs to be shedded.
Anya uses the line loading that would occur without shedding in the objective function. We could add this term or use the current without shedding in the line losses term. This might however not be a good idea, as this term is there to make the relaxation exact. On the other hand the relaxation doesn't need to be exact in our case as we are not using the power flow results but only the flexibility dispatch.