[AI Catalog] Rename read_ai_catalog policy to use_ai_catalog

What does this MR do and why?

Renames the read_ai_catalog policy to use_ai_catalog to better reflect its purpose.

With the ai_catalog_public_explore feature flag enabled, all users can now view/read the AI Catalog. However, only DAP users can take actions like enabling items, duplicating, or creating new items.

The name read_ai_catalog is now misleading since it implied read-only access, when it actually gates the ability to use/interact with the catalog.

• MR 1: !230916 (merged) - adds feature flag, makes page accessible to all users
• MR 2: !231096 (merged) - restricts actions to certain users
• MR 3 (this MR): !231099 (closed) - renames policy from read_ai_catalog to use_ai_catalog

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Related to #595123