Allow setting matplotlib.rcParams in monitor/multi_datasets.py

[schlunma]

Description

This PR allows setting matplotlib.rcParams in monitor/multi_datasets.py to have maximum control over plot appearance.

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New or updated recipe/diagnostic

• 🧪 Recipe runs successfully
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[schlunma]

@esmvalbot please run monitor/recipe_monitor_with_refs.yml

[esmvalbot]

Since @schlunma asked, ESMValBot will run recipe monitor/recipe_monitor_with_refs.yml as soon as possible, output will be generated here

[esmvalbot]

ESMValBot is happy to report recipe monitor/recipe_monitor_with_refs.yml ran OK, output has been generated here

[valeriupredoi]

cheers, Manu 🍺