add cmip7-prep to externals

[mnlevy1981]

The cmip7-prep tool provides scripts for CMORizing the data and other tasks necessary for preparing data for CMIP7. This PR adds it as an external, and also modifies the (cupid-analysis) environment to add the cmor python package, which also required updating the pinned versions of few other packages.

Description of changes:

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[mnlevy1981]

@jedwards4b if you drop this branch of CUPiD into $SRCROOT/tools/CUPiD and install (cupid-analysis) from it, you should be able to run all your cmip7-prep scripts out of $SRCROOT/tools/CUPiD/externals/cmip7-prep (you'll need to run git submodule update --init to populate externals/ before creating the environment)

[jedwards4b]

I have checked out the branch and updated the submodules, I don't understand "install (cupid-analysis) from it"

[mnlevy1981]

I have checked out the branch and updated the submodules, I don't understand "install (cupid-analysis) from it"

mamba env create -f environments/cupid-analysis.yml