poc for same-repo commenting

Author: berland

.github/workflows/backport.yml

@@ -0,0 +1,24 @@
+name: Comment on PR
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: read
+  pull-requests: write
+  issues: write
+
+jobs:
+  comment:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Add PR comment
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          REPO: ${{ github.repository }}
+        run: |
+          gh api \
+            "repos/$REPO/issues/$PR_NUMBER/comments" \
+            -f body='Image diff workflow ran successfully.'