Feature request: MOM6 assimilate scripting for CESM3

Use case

Scripting (assimilate) for MOM6 for cesm

Is your feature request related to a problem?

People want to use CESM3 beta (MOM6), so not a problem, just users.

Describe your preferred solution

Here is the scripting we have been using for CROCODILE (regional MOM6, but currently scripting is the same for DART)
https://github.com/CROCODILE-CESM/DART/blob/main/models/MOM6/cesm_scripts/assimilate.sh
This was to test cycling for use in Crocodile notebooks.
Still need to add inflation.

This is the routine in cime that calls the assimilate script:
https://github.com/ESMCI/cime/blob/d0b22795c9c3d2869d63964544f26e5e088a05bc/CIME/case/case_run.py#L420-L434

Note, since mostly we have been working with regional MOM6 which is under development, the filenames have been changing (see Enricos commits), so the output from MOM6 may not be in its final form.

Google doc notes on setting up mom6 cases - not I am not sure of the current supported CESM tags.
https://docs.google.com/document/d/1CGkvM_0CXy3b7gE2xiTEN2IcrTI9WDTGBR1UghIUIm4/edit?tab=t.0

Describe any alternatives you have considered

List any alternative solutions or workarounds you have considered.

• the run_or_sub routine will try to import python first:
  https://github.com/ESMCI/cime/blob/d0b22795c9c3d2869d63964544f26e5e088a05bc/CIME/utils.py#L680
  Currently just have a shell script. Using python would let you import the CIME stuff.

• There is a PRERUN and POSTRUN script if you look at the cime workflows documentation:
  https://esmci.github.io/cime/versions/master/html/users_guide/workflows.html
  which may be better for some setup/teardown stuff, but it actually looks like pre and post run are applicable to E3SM only:
  https://github.com/ESMCI/cime/blob/d0b22795c9c3d2869d63964544f26e5e088a05bc/CIME/case/case_run.py#L450-L469