Support `JuMP.set_parameter_value`

[pulsipher]

When solving JuMP models using the ExaModels optimizers it would be nice if parameter updates were directly supported. It seems that parameters are already created as such in the exafy conversions, but the update syntax is not supported. I think you just need to define something like:

function MOI.set(
    model::Optimizer,
    ::MOI.ConstraintSet,
    ci::MOI.ConstraintIndex{MOI.VariableIndex,MOI.Parameter{Float64}},
    set::MOI.Parameter{Float64},
)
   # TODO map to parameter and call ExaModels.set_parameter!
end

This would enable parameter updates without having to rebuild the the ExaModel.