Add artifact_registry backend service + access_artifact_registry UP

Adds catalog data so the Artifact Registry team can build an entitlement check around the gitlab_credits add-on. The Rails token-exchange endpoint (gitlab-org/gitlab!236798 (merged)) hardcodes the gitlab-artifact-registry audience and does not consume this catalog at runtime today, but the AR team's follow-up Ability (work-item gitlab-org/gitlab#599081) will:

up = ::Gitlab::CloudConnector::DataModel::UnitPrimitive.find_by_name(:access_artifact_registry)
::GitlabSubscriptions::AddOnPurchase.exists_for_unit_primitive?(up.name, user)

Without this UP in the catalog, that Ability can't exist.