Allow salt_flux_added to be used by generic tracers

[dougiesquire]

We've recently suggested changes to NOAA-GFDL/ocean_BGC generic_tracers to provide a way to pass the salt restoring/correction applied by the ocean model to generic tracers. Those proposed changes add a new subroutine generic_tracer::generic_tracer_update_from_coupler that receives the salt flux and passes it on the generic tracer's update_from_coupler routine if it is needed. Currently this feature is only utilised by the WOMBAT generic tracers which exist in the ACCESS-NRI fork of NOAA-GFDL/ocean_BGC.

To use this feature requires corresponding changes to the calling ocean model. In MOM6, the changes are as follows

• accumulate the added salt flux in MOM_forcing_type::fluxes_accumulate
• pass the accumulated flux to the new generic_tracer::generic_tracer_coupler_accumulate routine at the start of MOM_generic_tracer::MOM_generic_tracer_column_physics.

This PR implements these changes in ACCESS-OM3 via patches.

Note, it would be good in the long run to have these changes included in the authoritative MOM6. However, this should only happen if/when generic_tracer::generic_tracer_update_from_coupler is available in NOAA-GFDL/ocean_BGC.

[minghangli-uni]

Only one comment for the salt flux due to restoring or flux adjustment. Everythiing else looks good to me.

[minghangli-uni]

All clear to me! Thanks!