Add gitlab-templates code owners

With https://gitlab.com/gitlab-org/gitlab-ce/issues/50289 we moved CI
templates into gitlab repository.

The previous gitlab-ci-yml maintainers are now marked as code owners.
Auto DevOps is assigned to configure team backend developers.

.gitlab/CODEOWNERS

@@ -16,3 +16,5 @@ db/ @abrandl @NikolayS
 /ee/lib/gitlab/code_owners/ @reprazent
 /ee/lib/ee/gitlab/auth/ldap/ @dblessing @mkozono
 /lib/gitlab/auth/ldap/ @dblessing @mkozono
+/lib/gitlab/ci/templates/ @nolith @zj
+/lib/gitlab/ci/templates/Auto-DevOps.gitlab-ci.yml @DylanGriffith @mayra-cabrera @tkuah