Add DOGFOOD_OKTA_METADATA_URL to the dogfood GitOps workflow environment
and update SSO configuration to use Okta. it-and-security/default.yml:
change end_user_authentication.entity_id to fleet-end-users and org SSO
entity_id to fleet-admins, set idp_name to Okta for both, remove inline
metadata values, and point metadata_url to $DOGFOOD_OKTA_METADATA_URL.
This centralizes IdP metadata retrieval via a secret URL.