test: role privileges on vault objects and indexes

[steve-chavez]

Improves the previous tests while reducing britleness and revealing more implicit privileges.

• Reveals privileges on the _crypto_aead_det_* functions.
• Avoids testing the signature of functions (which was done by function calls), which is already done on z_15_ext_interface.out.

  supabase_vault         | vault                    | create_secret                                    | new_secret text, new_name text, new_description text, new_key_id uuid                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | uuid
  supabase_vault         | vault                    | update_secret                                    | secret_id uuid, new_secret text, new_name text, new_description text, new_key_id uuid                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | void

(https://github.com/supabase/postgres/blob/9bdefbcb7cc00b0692562c889b6c7d625120bd66/nix/tests/expected/z_15_ext_interface.out#L4754-L4755)

• Unique index test is added while also revealing the index owner.
• Avoids testing error messages, which can change across versions.
• Avoids testing implementation details, and reduces verboseness.