Add generation information to backports

backports/OpenTofu.gitlab-ci.yml

 # This template is a port of the OpenTofu CI/CD component at
 # https://gitlab.com/components/opentofu
+# It is generated with the `make backports` command from that project.
+#
 # Please make sure to use the component when your project is hosted on GitLab.com
 # or when you are willing to mirror the component project into your self-managed
 # instance and use it from there.