Generalizing FV3Forecast(Driver)

[benjamin-cash]

Hey everyone,

I've been reading through some of the code and had a couple of comments. After chatting with @christinaholtNOAA at AMS I'm putting them here so they are more available than just slack DMs. :) In FV3Forecast, there are a couple of places where things are hard coded - the required subdirectories (INPUT, RESTART) and the required config files in _prepare_config_files. Both of those are configuration dependent, and will need to be changed for the coupled model (for example). How difficult would it be to move those hard coded lists out into a configuration file and make that code reusable for other versions of the model?