Added CESM2 CMORizer

[schlunma]

Description

This PR implements a prototype of the on-the-fly CMORizer for the CESM2 model.

Link to documentation: https://esmvaltool--1678.org.readthedocs.build/projects/ESMValCore/en/1678/quickstart/find_data.html#cesm

Depends on #1718

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[codecov]

Codecov Report

Merging #1678 (b2af170) into main (4bb3061) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1678      +/-   ##
==========================================
+ Coverage   91.47%   91.48%   +0.01%     
==========================================
  Files         206      207       +1     
  Lines       11204    11218      +14     
==========================================
+ Hits        10249    10263      +14     
  Misses        955      955              

Impacted Files	Coverage Δ
esmvalcore/cmor/_fixes/cesm/cesm2.py	100.00% <100.00%> (ø)

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[remi-kazeroni]

Thanks for your contribution @schlunma, nice to have another model supported! This PR looks fine to me. Reusing shared fixes for native model output significantly reduces the number of code lines. I have a couple of minor suggestions, feel free to have a look. In particular, I would suggest to slightly expand the documentation to clarify which variables are currently supported and maybe how support could be added in the future for other cases.

[schlunma]

Thanks for the review @remi-kazeroni! I expanded the doc and addressed all your comments. Let me know if you need anything else! 👍

[remi-kazeroni]

Thanks for the changes @schlunma! This looks good to me as it is 👍

[valeriupredoi]

fellas @schlunma @remi-kazeroni I am ready to merge this if there are no major objections so I can include it in the 2.7 freezer ☃️ Please yell at me if otherwise, if not I will merge it by the end of day today 👍

[valeriupredoi]

OK fellas, she's going in 🚢

[schlunma]

Thanks V! Sorry for the late reply, we had a public holiday yesterday 😄