`relation_cost` is not included in the calculation of `levelized_cost`

`levelized_cost` is used to calculate the penalty for the activation of soft constraints in the model. While the equation calculating `levelized_cost` should include all cost related parameters for technologies (see [message_ix/model/MESSAGE/scaling_investment_costs.gms](url)), it omits `relation_cost`. This can underestimate the penalty for those technologies that have cost associated to their capacity or activity, represented via `relation_cost`.