add review "app"

but instead of deploying to a live environment,
simply link to the landing page in the artifacts.
This adds a "View app" button to merge requests,
making it easier to review the respective build results.

.gitlab-ci.yml

@@ -16,6 +16,9 @@ pages: &pages_job
   artifacts:
     paths:
       - public
+  environment:
+    name: review/$CI_COMMIT_REF_NAME
+    url: ${CI_PROJECT_URL}/-/jobs/artifacts/${CI_COMMIT_REF_NAME}/file/public/index.html?job=${CI_JOB_NAME}
 
 pages_without_deployment:
   <<: *pages_job