ci: add a final dd-gitlab/finished job

.gitlab-ci.yml

@@ -55,3 +55,16 @@ deploy_to_di_backend:manual:
     UPSTREAM_COMMIT_AUTHOR: $CI_COMMIT_AUTHOR
     UPSTREAM_TAG: $CI_COMMIT_TAG
     UPSTREAM_PACKAGE_JOB: build
+
+
+# Final step which only runs when a pipeline has finished successfully.
+# This gives us something block on/wait for in GitHub
+finished:
+  image: registry.ddbuild.io/images/mirror/library/alpine:3.19.3
+  tags: [ "arch:amd64" ]
+  stage: .post
+  rules:
+    - when: on_success
+  script:
+    # TODO: Can we get this to reflect the status from the whole pipeline?
+    - exit 0