RRFS-MPAS applications: add several fields to output; remove "imp_physics" logic from INITPOST_MPAS

[jaymes-kenyon]

This PR addresses issue #1087 for MPAS applications. Namely:

• For VIL, discontinue use of the local GRIB2 table
• Add GSL's experimental ceiling fields to the GRIB2 output

Additionally, within "INITPOST_MPAS", many instances "if imp_physics..." are removed. These portions of the code (originally inherited from "INITPOST") initialize various hydrometeor arrays based upon the microphysics scheme. However, many of these "imp_physics" identifiers correspond to schemes in WRF-ARW and may not have relevance for MPAS. If future MPAS development requires this logic, then similar code structures can be re-introduced.

[WenMeng-NOAA]

@jaymes-kenyon I ran an UPP standalone test with MPAS data files you provided at /home/Wen.Meng/stmp2/mpas_2024082112-after on Hera. Can you take a look at it and let me know if you see issues?
The three new fields you are proposing have been generated in WRFTWO dataset as:

3:1190255:ndata=1905141:undef=0:mean=0.143845:min=0:max=76.18:cos_wt_mean=0.144931:d=2024082100:VIL:entire atmosphere:12 hour fcst:
113:70778438:ndata=1905141:undef=827150:mean=4332.37:min=23.9683:max=14617.5:cos_wt_mean=4394.42:d=2024082100:CEIL:cloud ceiling:12 hour fcst:
114:73009041:ndata=1905141:undef=0:mean=11423.9:min=23.9683:max=20000:cos_wt_mean=11497.2:d=2024082100:CEIL:cloud base:12 hour fcst:

[jaymes-kenyon]

@WenMeng-NOAA — Thanks! Your test results look good; these are are new fields that are expected from this PR. Thanks for sharing!

[WenMeng-NOAA]

@gspetro-NOAA This PR is ready for the UPP RTs. There should be no baseline changes.

[WenMeng-NOAA]

The UPP RTs have been completed on WCOSS2 with no baseline changes.