generate_user_access_token was copy-pasted in seven test modules
(user access token authentication, and rooms create, list, retrieve,
update, participants management, rename/toggle and subtitle).
Extract it into core.tests.utils and reuse it everywhere. The shared
version keeps the optional application and claim overrides from the
authentication tests, and reads the token type claim from
USER_ACCESS_TOKEN_TYPE_CLAIM instead of hardcoding it.
lebaudantoine