Add ABI L2 Low Cloud and Fog products

[djhoese]

• IFR Probability
• Low IFR Probability
• MVFR Probability
• Cloud/Fog thickness

This is different than the other L2 products as these files aren't supported in Satpy yet. These files also follow a different structure than other PUG files. Filenames from CSPP Geo look like:

GOES16_ABI_2KM_MESO_2019147_1800_48_AVIATION_FOG_EN.nc

And from NDE/CLASS:

ABI-L2-GFLSC-M6_v3r1_g16_s202306071931181_e202306071933554_c202306071934440.nc

Colormaps should probably follow the AWIPS colormaps which should match the algorithm team's preferred colormaps.

Possible useful information:

https://vlab.noaa.gov/web/towr-s/goes-16-fog-and-low-stratus

[djhoese]

The initial version of this has been added now. Any future issues or changes will be in other issues or pull requests.

Note the NDE files are not currently supported. They have informed us of two versions of the files: The original files had Longitude/Latitude arrays instead of grid mapping projection information and the dimensions are named ("Rows", "Columns"). Supporting these files unrealistic without "hacks" to hardcode the geolocation information. The other files are a slimmed down version of the original that have the grid mapping, have y/x dimensions, but are lacking some global attributes. These files are also 16-bit integers for the data variables, but those work out of the box in the Satpy reader.

Bottom line: G2G only supports the CSPP Geo AIT version of the files (grid mapping, y/x dimensions, full global attributes).