Get scene communication adapter

Generates LiveKit credentials for a user to join a scene's communication room. This endpoint handles authentication, blacklist checking, scene ban verification, and generates appropriate permissions for the user. Requires Signed Fetch authentication from decentraland-kernel-scene. Must include the complete identity header chain: x-identity-auth-chain-0, x-identity-auth-chain-1, x-identity-auth-chain-2, x-identity-timestamp, and x-identity-metadata.