Modern_diag_manager:: flush_nc_files is not implemented in the new diag manager

[uramirez8707]

Is your feature request related to a problem? Please describe.
flush_nc_files=.true. has not been implemented in the new diag manager and it would not work:

FMS/diag_manager/diag_data.F90

Lines 365 to 370 in d3bab5a

	LOGICAL :: flush_nc_files = .FALSE. !< Control if diag_manager will force a
	!! flush of the netCDF file on each write.
	!! Note: changing this to .TRUE. can greatly
	!! reduce the performance of the model, as the
	!! model must wait until the flush to disk has
	!! completed.

Describe the solution you'd like
flush_nc_files=.true. should work as it did with the old diag manager.

Describe alternatives you've considered
N/A

Additional context
N/A

[uramirez8707]

Fixed in #1506