recreate perfmetrics portrait plot in python

[lukruh]

Description

• Closes Recreate portrait plot from NCL perfmetrics in python #3550
• Link to documentation:

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• ☝ Create an issue to discuss what you are going to do Recreate portrait plot from NCL perfmetrics in python #3550

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[valeriupredoi]

what a noble venture, Lukas! Godspeed 🏁 🍺

[bettina-gier]

Some minor changes needed, mostly in documentation.

Also requires ESMValGroup/ESMValCore#2564 to run with a current core bug on multi-model statistics.

[lukruh]

The recipe runs again with ESMValGroup/ESMValCore#2564. Should we wait for it before merging this?

@schlunma I adressed all your review comments. If you have time to re-review it, that would be awesome.

I added a cheaper version of the recipe to the recipes/testing folder. Is that the correct way to provide a test version? Should I also add it to RTW?