[ci] Do not run pipelines for workflow:paused labeled MRs.

.gitlab-ci.yml

@@ -23,6 +23,8 @@ workflow:
     # Disable CI for non-MR user-scoped pipelines
     - if: '$CI_MERGE_REQUEST_IID == null && $CI_PROJECT_NAMESPACE != "ogs"'
       when: never
+    - if: '$CI_MERGE_REQUEST_LABELS =~ /.*workflow:paused.*/'
+      when: never
     - if: $CI_MERGE_REQUEST_IID                    # merge requests
     - if: $CI_COMMIT_TAG                           # tags, ogs/ogs repo only
     - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH  # master, ogs/ogs repo only