Change PR to draft when it is (re)opened (#36417)

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Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

.github/workflows/change_pr_to_draft.yml

@@ -0,0 +1,22 @@
+name: Change PR to draft
+
+on:
+  pull_request_target:
+    types: [opened, reopened]
+
+jobs:
+  convert_pr_to_draft:
+    runs-on: ubuntu-22.04
+    name: Convert PR to draft
+    if: github.event.pull_request.draft == false
+    steps:
+      - name: Convert PR to draft
+        shell: bash
+        env:
+          PR_NUMBER: ${{ github.event.number }}
+          GH_TOKEN: ${{ github.token }}
+          REPO: ${{ github.repository }}
+        run: |
+          echo $PR_NUMBER
+          gh pr ready $PR_NUMBER --repo $REPO --undo
+          gh pr comment $PR_NUMBER --repo $REPO --body "Hi 👋, thank you for opening this pull request! The pull request is converted to draft by default. When it is ready for review, please click the \`Ready for review\` button (at the bottom of the PR page)."