docs: define the authorization catalog API

[mariajgrimaldi]

Description

The existing roles endpoint returns role and permission identifiers from Casbin, but it does not return the display names, descriptions, categories, icons, or definition source needed by clients. Frontends therefore keep their own copies, so a role contributed by an application can still require a frontend release.

This ADR extends the AuthZ APIs to return the authorization definitions stored in the authz model. Clients can use the same endpoint for static and user-defined roles, receive translated display metadata, and continue using the existing response fields.

Merge checklist:
Check off if complete or not applicable:

• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Fixup commits are squashed away
• Unit tests added/updated
• Manual testing instructions provided
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

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