Add the possibility to set tollerances on equality constraints for TSID

[Gio-DS]

It would be nice to have the possibility to set some tollerances on equality constraints of blf TSID optimization problem. The idea would be to turn equality constraints into inequality constraints by setting a tollerance $\delta$:

$$Ax = b \rightarrow b-\delta \leq Ax \leq b+ \delta$$

CC @xela-95

[GiulioRomualdi]

I would avoid using this approach and I will go for slack variables this will also allow us in the future to close #529