Add tags / tags filtering to Area filter

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Similar to what we did to the new species selector.

This is a request by @damianooldoni because the list of available areas will increase soon.

Implementation question: do we generalize the species selector so we gain all the features in one shot (filter by text, select all, ...)? At first look it would be better (but also a bit more complex than "just adding tags to areas")

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Backend: tags added.

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Recently also implemented in frontend