nuopc_driver updates (mom-ocean#22)

* allows control of MOM6 restarts and MOM6 intermediate restarts using nems.configure settings restart_n and restart_option. Fixes duplicate restart issue when running with CMEPS (mom-ocean#16).
* when field dumping is turned on, all fields in import state and export state are written to single file with timestamped file name (mom-ocean#15)
* moves call to data_override field lrunoff out of the enclosing do loop (mom-ocean#21 )


Co-authored-by: Mariana Vertenstein <mvertens@ucar.edu>

Author: DeniseWorthen