UFS-AQM related readers

[zmoon]

We have a number of readers that seem to be related to UFS-AQM and its predecessors.

• https://github.com/noaa-oar-arl/monetio/blob/develop/monetio/models/_cmaq_mm.py
• https://github.com/noaa-oar-arl/monetio/blob/develop/monetio/models/_rrfs_cmaq_mm.py
• https://github.com/noaa-oar-arl/monetio/blob/develop/monetio/models/cmaq.py
• https://github.com/noaa-oar-arl/monetio/blob/develop/monetio/models/fv3chem.py
• https://github.com/noaa-oar-arl/monetio/blob/develop/monetio/models/ncep_grib.py

Maybe for v0.3 we can combine some of these or remove ones that are no longer relevant.

cc: @bbakernoaa @rschwant @drnimbusrain