Add SNOWC to RRFS grib2 output

[BenjaminBlake-NOAA]

DESCRIPTION OF CHANGES:

• The SNOWC field is added to the RRFS grib2 output files (not subhourly output). This parameter is available in the HRRR and NAM nest. All of the postcntrl xml and postxconfig flat files have been updated accordingly.

TESTS CONDUCTED:

Ran an offline UPP test (outside of the workflow) and confirmed that SNOWC was available with reasonable values in the grib2 output files.

Machines/Platforms:

• WCOSS2
  • Cactus/Dogwood
  • Acorn
• RDHPCS
  • Hera
  • Jet
  • Orion
  • Hercules

Test cases:

• Engineering tests
  • Non-DA engineering test
  • DA engineering test
    • Retro
    • Ensemble
    • Parallel
• RRFS fire weather
• RRFS_A:
• RRFS_B:
• RTMA:
• Others: UPP driver script

ISSUE:

• Fixes issue Add SNOWC to RRFS grib2 output #634

[MatthewPyle-NOAA]

Looks good to me. Thanks, Ben!