Add variable dimensions to available_diags file

[jkrasting]

The output of the current available_diags file lacks the dimensions of each diagnostic.

This PR includes a commit that adds the appropriate horizontal and vertical dimension names to the entries listed in the available_diags file. Scalar diagnostics are denoted with a "scalar" string.

Example of an entry generated with the new code:

"temp"  [Used] (CMOR equivalent is "thetao")
    ! modules: {ocean_model,ocean_model_z,ocean_model_rho2,ocean_model_rho0,ocean_model_d2,ocean_model_z_d2,ocean_model_rho2_d2,ocean_model_rho0_d2}
    ! dimensions: yh, xh, zl
    ! long_name: Potential Temperature
    ! units: degC
    ! cell_methods: xh:mean yh:mean zl:mean area:mean
    ! variants: {temp,temp_xyave,thetao,thetao_xyave}

[marshallward]

Apologies for moving the goalposts, but if we're considering revisions to available_diags, then we could also convert it to YAML:

temp:
    used: True
    cmor_equivalent: thetao
    modules: [ocean_model, ocean_model_z, ocean_model_rho2, ocean_model_rho0, ocean_model_d2, ocean_model_z_d2, ocean_model_rho2_d2, ocean_model_rho0_d2]
    dimensions: [yh, xh, zl]
    long_name: Potential Temperature
    units: degC
    cell_methods: [xh:mean, yh:mean, zl:mean, area:mean]
    variants: [temp, temp_xyave, thetao, thetao_xyave]

This would make postprocessing easier for many people.

[codecov]

Codecov Report

Attention: Patch coverage is 51.51515% with 16 lines in your changes missing coverage. Please review.

Project coverage is 36.79%. Comparing base (0daa4ff) to head (75307c5).
Report is 1 commits behind head on dev/gfdl.

Files with missing lines	Patch %	Lines
src/framework/MOM_diag_mediator.F90	51.51%	0 Missing and 16 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           dev/gfdl     #864      +/-   ##
============================================
- Coverage     38.01%   36.79%   -1.22%     
============================================
  Files           298      290       -8     
  Lines         87986    86927    -1059     
  Branches      16521    16524       +3     
============================================
- Hits          33447    31989    -1458     
- Misses        48483    48834     +351     
- Partials       6056     6104      +48     

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[jkrasting]

@Hallberg-NOAA - I reordered the dimensions and improved the string trimming logic as you suggested.

[Hallberg-NOAA]

These proposed changes look good to me. Thank you for this valuable new contribution.

[Hallberg-NOAA]

This PR has passed pipeline testing at https://gitlab.gfdl.noaa.gov/ogrp/mom6ci/MOM6/-/pipelines/26893 with the expected warnings about changes to the available diags file metadata.