Allocation optimization with main network

[SouthEndMusic]

What
This is issue is for completing the main structure of allocation optimization.

How
There are the following steps:

• I think it is quite straightforward to support a model that does not have a main network, where allocation is only solved in one subnetwork. This can be handled with a simple if statement in update_allocation!. To check whether the model has a subnetwork, use the following function:

function has_main_network(allocation::Allocation)::Bool
   return first(allocation.allocation_network_ids) == 1
end

This should always work given the ordering of the allocation network IDs and the validation introduced in #710.

• Add a kwarg collect_demands::Bool = true to the function allocate!. If collect_demands == false the function should behave as it currently does, otherwise:

• In adjust_source_flows!, make sure the capacities of the sources that are connections from the main network to the subnetwork are set to $\infty$ (or deactivate the source constraints entirely if possible);

• In assign_allocations!, make sure the allocations are written to allocation.subnetwork_demands instead of user.allocated.

• At the beginning of update_allocation!, loop over the allocation models of the subnetworks to compute the subnetwork demands, i.e. call allocate! on the subnetworks with collect_demands = true.

• In set_objective_priority!, make sure that for the main network allocation the subnetworks are also reflected in the objective function, with the demands coming from allocation.subnetwork_demands.

• In adjust_source_flows! for a subnetwork when collect_demands = false, for sources that come from the main network, make sure that the source capacity is set to what is allocated to that edge in the main network problem.

• Add tests:

• Test whether the optimization problem for the main network is correct;

• Test whether not more water is allocated within the subnetwork than is allocated to the subnetwork from the main network;.

• running the main_network_with_subnetworks test model to completion with succesful_retcode.