Introduce GEOM_FILE runtime parameter to set ocean_geometry file name.

[alperaltuntas]

This is to enable the prefixing of the ocean geometry file with the case (experiment) name, and thus enable adherence to CESM output file naming convention and allow short term archiving of ocean_geometry file.

testing: SMS.TL319_t232.GMOM_JRA.derecho_gnu

[klindsay28]

In our existing diagnostic/history output, 2D fields on the tracer grid have the attribute
cell_measures = "area: areacello"
and the files have a global attribute
associated_files = "areacello: $CASENAME.mom6.h.static.nc".
This CF convention based metadata enables analysis scripts and notebooks to use the get the proper cell area without hardcoding area variable names.

With the present codebase, we lose this if we rely on getting area from the geometry file. Area in the geometry file is called "Ah", which doesn't match the cell_measures attribute, and the geometry file filename doesn't appear in the associated_files file attribute.

The name Ah is hardcoded in MOM6 write_ocean_geometry_file in src/initialization/MOM_shared_initialization.F90.

Perhaps we discuss this in the next MOM6 dev call.

I don't think that this concern should hold up this PR.