Add Delivery as an owner of the release config

Since changes to this file directly affect the Delivery team, it makes
sense that they own this file and approve any changes to it.

.gitlab/CODEOWNERS

@@ -43,3 +43,6 @@ Dangerfile @gl-quality/eng-prod
 /danger/ @gl-quality/eng-prod
 /lib/gitlab/danger/ @gl-quality/eng-prod
 /scripts/ @gl-quality/eng-prod
+
+# Delivery owner files
+/.gitlab/ci/releases.gitlab-ci.yml @gitlab-org/delivery