Add rho and surface variables in zrecast outputs

[abierjon]

While rho is a 4D variable, when we use zrecast to have Pressure coordinates, it is not present in the outputs (without telling it to the user)

+ it would give the opportunity to add surface/3D variables in the outputs, which are now skipped and force us to work sometimes with 2 files

[abierjon]

Actually, rho is well in the outputs