Add functionality to run single diagnostic task to notebook API

[stefsmeets]

Description

Hi everyone, this PR extends the API to run recipes in an interactive notebook.

It adds functionality to list and run a single diagnostic task, and display/load the output directly in the notebook. I also cleaned up some long references in the API documentation.

• For more discussion, see issue ESMValCore (and ESMValTool) Python/Jupyter Notebook API #498
• Follows up on Add displaying and loading of recipe output to the notebook API #957, Add loading and running recipes to the notebook API #907, Add Listing and finding recipes to the experimental notebook API #901, Implement importable config object in experimental API submodule #868
• Link to documentation: https://esmvaltool--962.org.readthedocs.build/projects/ESMValCore/en/907/api/esmvalcore.api.html
• Demo notebook: https://gist.github.com/stefsmeets/876c1743a98101dd4774eb959c7afafd

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Checklist

• PR has a descriptive title for the changelog
• Code follows the style guide
• Documentation is available for new functionality
• YAML files pass pre-commit or yamllint checks
• Circle/CI tests pass
• Codacy code quality checks pass
• Documentation builds successfully on readthedocs
• Unit tests are available

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[stefsmeets]

Hi @Peter9192 , it turned out to be more or less 1 line of code after all 😅 Could you have a look and let me know what you think?

[Peter9192]

This works super smooth! Nice job :-)
One question about the docs formatting and one typo I think.

[stefsmeets]

Thanks @Peter9192 !

This is now ready to be merged! @nielsdrost @bouweandela

[nielsdrost]

Thanks @Peter9192 and @stefsmeets!