FEATURE - ENSEMBLE_MANAGER: Better ensemble support

[uramirez8707]

Is your feature request related to a problem? Please describe.
SPEAR runs multiple ensembles (>30). For high resolutions runs, it is impossible to run all 30 ensemble at a time, so they instead create an experiment for each group. (i.e experiment 1 runs ens01-03, experiment 2 runs ens04-06, etc)

When the output is created the files are appended with ensXX to the filename (i.e my_file.ens_01.nc). However, the ensemble manager has no way of knowing that experiment starts with 04 and not 01, so even though experiment 2 is running ens04-06 its output will have ens01-03 in the name. This causes extra messy PP steps.

Describe the solution you'd like
Add a namelist to the ensemble manager starting_ensemble_number
Then, when sending in the ensemble number to fms2io, it will be based on this number.

FMS/coupler/ensemble_manager.F90

Lines 403 to 407 in 59763e9

	if (ensemble_size > 1) then
	write( text,'(a,i2.2)' ) 'ens_', ensemble_id
	!Append ensemble_id to the restart filenames
	call fms2_io_set_filename_appendix(trim(text))
	endif

For example, for experiment 2 starting_ensemble_number will be 4, so it will be

write( text,'(a,i2.2)' ) 'ens_', starting_ensemble_number + ensemble_id - 1

Describe alternatives you've considered
N/A

Additional context
N/A