Add support for MOI.ConstraintConflictStatus of SOS constraints

[sebastianangerhausen]

If a model containing SOS2 constraints is infeasible and the IIS is computed, copying the conflict model leads to the following error:

ERROR: LoadError: MathOptInterface.GetAttributeNotAllowed{MathOptInterface.ConstraintConflictStatus}: Getting attribute MathOptInterface.ConstraintConflictStatus() cannot be performed: Gurobi.Optimizer does not support getting the attribute MathOptInterface.ConstraintConflictStatus(). You may want to use a CachingOptimizer in AUTOMATIC mode or you may need to call reset_optimizer before doing this operation if the CachingOptimizer is in MANUAL mode.

This is a minimal example to reproduce the error:

using JuMP, Gurobi

model = Model(Gurobi.Optimizer)

@variable(model, x[1:3] ≥ 0)

# SOS2 constraint
@constraint(model, x in SOS2())

# additional constraint to create infeasibility
@constraint(model, sum(x) == -1)

@objective(model, Min, sum(x))

optimize!(model)

compute_conflict!(model)

# this line produces the error
iis_model, _ = copy_conflict(model)

I am using Julia v1.10, JuMP v1.23.6, and Gurobi v1.6.1 on Windows.

[odow]

We need this attribute: https://docs.gurobi.com/projects/optimizer/en/current/reference/attributes/sos.html#attriissos