Monthly output instead of daily / nstep

[mnlevy1981]

Currently FEISTY is just dumping output to netcdf at the end of every time step; monthly averages should be sufficient and will reduce output size by quite a bit.

[mnlevy1981]

Kristen was converting from daily to monthly in postprocessing with

ds_mon = ds_out.resample({'time':'M'}).mean(dim='time')

A first pass to this issue could be including a resample_output flag in the output portion of the configuration file and then updating ds_out after the call to config_and_run_from_dataset() but prior to writing the output (well, we'd want to write the restart file then resample then write the history file)