Add an `esmvaltool recipes expand` command to expand wildcards in the recipe (once we support them better)

[bouweandela]

Add an esmvaltool recipes expand command to expand wildcards in the recipe (once support them better), without actually running the recipe.

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[github-actions]

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[bouweandela]

In case anyone is looking for an alternative for this command that was not implemented, we have a Jupyter notebook available here: https://github.com/ESMValGroup/ESMValCore/blob/main/notebooks/composing-recipes.ipynb

See also ESMValGroup/ESMValTool#4106 (reply in thread)