docs(api-keys): clarify set vs item permissions for synonym and curation sets

[tharropoulos]

Change Summary

• update API key action tables in 30.0 and 30.1 to include /items actions under both synonym_sets and curation_sets.
• note about permission boundaries: item-level actions are separate from set-level actions (for example, *: * on sets does not automatically include /items:).
• feedback from [Question] Permission scoping not related to collections typesense#2818 (comment)

PR Checklist

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[prmaxim]

Hi @tharropoulos, @jasonbosco could you also take a look at #445? It includes the related updates for new synonyms and curations. Thanks!