Add the "publish" job

Add a new SSH-confirmed GitLab CI job that publishes a previously staged
release to a well-known URL.  The details of what specifically this
entails are controlled by the staging environment.

.gitlab-ci.yml

@@ -1734,6 +1734,23 @@ publish-private:
   rules:
     - if: '$CI_COMMIT_TAG != null && ($CI_COMMIT_TAG =~ /-S/ || $RELEASE_TYPE == "security")'
 
+# Job copying a staged release to a well-known location
+
+publish:
+  <<: *signer_ssh_job
+  variables:
+    SSH_SCRIPT_CLIENT: |-
+      ssh "${STAGING_USER_ACTIONS}@${STAGING_HOST}" "publish ${CI_COMMIT_TAG}"
+  artifacts:
+    paths:
+      - publish-${CI_COMMIT_TAG}.log
+    expire_in: "1 month"
+  needs:
+    - job: staging
+      artifacts: false
+  rules:
+    - if: '$CI_COMMIT_TAG != null && $CI_COMMIT_TAG !~ /-S/'
+
 # Job creating the release announcement MR in Printing Press
 
 prepare-release-announcement: