Forcing variable names set in namelist.hrldas

[barlage]

To add flexibility in the forcing files, allow generic naming for the forcing variables. These are set in the namelist.hrldas. This has a few benefits:

1. forcing names can be more descriptive
2. multiple sources for the same forcing can be present and the namelist chooses which to use

Expected Behavior

Forcing files can have any variable names and they are determined by namelist settings.

Current Behavior

Forcing variables are required to have predetermined names.

Possible Solution

See:

https://github.com/barlage/wrf_hydro_nwm_public/tree/forcing_generic

[barlage]

This branch is a transfer of current HRLDAS capabilities and solves my current needs in WRF-Hydro but needs to be more general for WRF_Hydro forcing.