Use slug as the prefix for the docs CI job preview URL

.gitlab-ci.yml

@@ -193,7 +193,7 @@ review-docs-deploy:
     name: review-docs/$CI_COMMIT_REF_NAME
     # DOCS_REVIEW_APPS_DOMAIN and DOCS_GITLAB_REPO_SUFFIX are secret variables
     # Discussion: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14236/diffs#note_40140693
-    url: http://preview-$CI_COMMIT_REF_SLUG.$DOCS_REVIEW_APPS_DOMAIN/$DOCS_GITLAB_REPO_SUFFIX
+    url: http://$DOCS_GITLAB_REPO_SUFFIX-$CI_COMMIT_REF_SLUG.$DOCS_REVIEW_APPS_DOMAIN/$DOCS_GITLAB_REPO_SUFFIX
     on_stop: review-docs-cleanup
   script:
     - ./trigger-build-docs deploy

scripts/trigger-build-docs

@@ -27,7 +27,7 @@ def docs_branch
   # Prefix the remote branch with 'preview-' in order to avoid
   # name conflicts in the rare case the branch name already
   # exists in the docs repo and truncate to max length.
-  "preview-#{ENV["CI_COMMIT_REF_SLUG"]}"[0...max]
+  "#{slug}-#{ENV["CI_COMMIT_REF_SLUG"]}"[0...max]
 end
 
 #