Ice-shelf solo driver and MISMIP+ updates

[alex-huth]

-Several edits to the ice shelf solo driver so that it works with the rest of the current MOM6
-Added capability to initialize a surface mass balance (SMB) that is held contstant over time when running from the ice-shelf solo driver (see new subroutine initialize_ice_SMB). This is required for MISMIP+. A constant SMB can also be used from the MOM driver for coupled ice-shelf/ocean experiments (e.g. MISOMIP).
-The new, constant SMB is passed into solo_step_ice_shelf, where change_thickness_using_precip is called
-Added capability to save both non-time-stamped and time-stamped restart files when using the ice shelf solo driver. This is useful for debugging.
-slight reorganization to when ice shelf post_data calls are made

[codecov]

Codecov Report

Merging #471 (4125523) into dev/gfdl (475590d) will decrease coverage by 0.05%.
The diff coverage is 12.69%.

❗ Current head 4125523 differs from pull request most recent head 7cd5e8d. Consider uploading reports for the commit 7cd5e8d to get more accurate results

@@             Coverage Diff              @@
##           dev/gfdl     #471      +/-   ##
============================================
- Coverage     37.83%   37.79%   -0.05%     
============================================
  Files           270      270              
  Lines         78346    78375      +29     
  Branches      14502    14533      +31     
============================================
- Hits          29643    29622      -21     
- Misses        43296    43318      +22     
- Partials       5407     5435      +28     

Files	Coverage Δ
src/ice_shelf/MOM_ice_shelf_dynamics.F90	0.00% <0.00%> (ø)
config_src/drivers/solo_driver/MOM_driver.F90	50.62% <0.00%> (-0.43%)	⬇️
src/ice_shelf/MOM_ice_shelf.F90	0.00% <0.00%> (ø)
src/ice_shelf/MOM_ice_shelf_initialize.F90	0.00% <0.00%> (ø)
src/framework/MOM_diag_mediator.F90	57.50% <22.22%> (-1.32%)	⬇️

... and 1 file with indirect coverage changes

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[Hallberg-NOAA]

I do not understand why we need a separate solo_ice_shelf_diag_mediator_end() routine in MOM_diag_mediator.F90 that is distict from diag_mediator_end(). They appear to me to take the same arguments and do the same thing, perhaps with a little error checking. Given that they are so similar, why not add the safety checks to diag_mediator_end()?

Also, the capability being added with the new runtime parameter SAVE_BOTH_RESTARTS could already have been obtained by setting RESTART_CONTROL=3. The new parameter may be more explicit, but it does add to the list of parameters without actually adding any new capabilities.

[alex-huth]

I revised the PR as suggested by @Hallberg-NOAA . I added safety checks to diag_mediator_end() so that the separate solo_ice_shelf_diag_mediator_end() routine is no longer necessary. I also removed the SAVE_BOTH_RESTARTS option, which was useful during development, but is not needed anymore.

[Hallberg-NOAA]

This set of code changes looks reasonable to me.