Time varying values for array parameters

[DillonJ]

In https://github.com/spine-tools/SpineOpt.jl/issues/545 @elinaspyrou points out that you can have a time varying value for fix_unit_flow_op because the value needs to be an array.

Other than being able to define the initial value via initial_unit_flow_op, I believe time varying arrays isn't something we support right now (right @manuelma ?). Perhaps the way to support it would be via maps somehow and I believe this would require some work in SpineInterface.

Thoughts @manuelma ?

[DillonJ]

@manuelma for information, @elinaspyrou has posted some additional information in the original issue here: https://github.com/spine-tools/SpineOpt.jl/issues/545

[clizbe]

Sounds like a Nice to Have since there's a work-around