Bring the file extension (.json|.nc) into an option

[jameshalgren]

On this line,

nwmurl/nwmurl/urlgennwm.py

Line 490 in aadafa3

file.write(f"{item}.json\n")

we might consider using a default file extension in a variable that we pass into the function call. That way, if someone comes up with parquet files or some other extension, we don't have issues with that.

[sepehrkrz]

File extensions depend on the urlbaseinput chosen value and it is already determined in the code based on that value.

[jameshalgren]

Perhaps we can make this a bit more modular in a refactoring pass.