Allow different advection schemes for momentum and tracers in `NonHydrostaticModel`

[xkykai]

Currently, NonHydrostaticModel does not support specifications for momentum_advection and tracer_advection. It would be nice to include a feature like this, as has been implemented in the HydrostaticFreeSurfaceModel.

@simone-silvestri

[glwagner]

Agree, someone should work on that 😄