Read domain data directly from geo_em file

[mkavulich]

It is often inconvenient to have to provide a namelist text file to update the fire fields. All of the information needed to add NFUEL_CAT (fuel category) and ZSF (terrain) fields for the fire domain is contained within the geo_em.dXX.nc file, so we should add the option to read the information directly from there

[mefrediani]

This is only true if the geogrid file already has a fire subgrid. If not, subgrid_ratio_x/y are not there. This is one of the issues my draft PR addressed, calculating the subgrid domain when one is not available. However, there's more in that PR and I don't know if my intended goal is gonna work, so the rest of the PR may be irrelevant.

[mefrediani]

After some experimentation I realize it's simpler and more error safe to run geogrid with subgrid_ratio_x/y. If the namelist option is there, it will create the subgrid even it we don't provide fuels and zsf. Then fire_preprocess can handle the fields afterwards. Running geogrid is quick, so that caveat can be disregarded.