[PATCH 3/4] auth: db-oauth2: Add oauth2_audience setting, deprecate aud-as-scope...

[PATCH 3/4] auth: db-oauth2: Add oauth2_audience setting, deprecate aud-as-scope fallback

Add a dedicated oauth2_audience setting checked against the token's aud
claim (RFC 7519 section 4.1.3) using the same tab-split AND-semantics as
oauth2_scope. Emit a deprecation warning when the existing aud fallback
in db_oauth2_token_in_scope() is triggered so operators know to migrate.

Gbp-Pq: Name 0003-auth-db-oauth2-Add-oauth2_audience-setting-deprecate.patch