Force explicit computation of sigma_crit in galaxycluster object

[m-aguena]

Currently, GalaxyCluster functions that require sigma_c (or sigma_c_eff) compute them implicitly when needed. We should force the user to make the explicit computation using GalaxyCluster.add_critical_surface_density so it is clear where it is coming from and to make it more symmetric with the functional interface. Discussed in https://github.com/LSSTDESC/CLMM/pull/596#issuecomment-1634217956