Add support for equality constraints in DenseCondensedKKTSystem

[frapac]

Right now, the option DENSE_CONDENSED_KKT_SYSTEM does not reduce the equality constraints and focuses only on the inequality constraints. One has to use an elastic relaxation to reformulate the equality constraints as inequalities before condensing the system.

We should investigate a proper way to condense both the equality and the inequality constraints, without resorting to an elastic relaxation trick.

[sshin23]

maybe create a new option condense_equality_constraints=true and apply elastic relaxation only if this option is true?