add: github backport action

.github/workflows/backport-pr.yml

@@ -0,0 +1,37 @@
+name: Backport PR
+on:
+  pull_request_target:
+    types:
+      - closed
+      - labeled
+
+jobs:
+  backport:
+    name: Backport PR
+    runs-on: ubuntu-latest
+    if: >
+      github.event.pull_request.merged
+      && (
+        github.event.action == 'closed'
+        || (
+          github.event.action == 'labeled'
+          && contains(github.event.label.name, 'backport')
+        )
+      )
+    steps:
+      - uses: actions/create-github-app-token@7bfa3a4717ef143a604ee0a99d859b8886a96d00 # v1.9.3
+        id: app-token
+        with:
+          app-id: ${{ vars.DD_GITHUB_TOKEN_GENERATOR_APP_ID }}
+          private-key: ${{ secrets.DD_GITHUB_TOKEN_GENERATOR_PRIVATE_KEY }}
+      - uses: tibdex/backport@9565281eda0731b1d20c4025c43339fb0a23812e # v2.0.4
+        with:
+          label_pattern: "^backport/(?<base>([^ ]+))$"
+          labels_template: "<%= JSON.stringify([...labels, 'backport', 'bot']) %>"
+          github_token: ${{ steps.app-token.outputs.token }}
+          body_template: |
+            Backport <%= mergeCommitSha %> from #<%= number %>.
+
+            ___
+
+            <%= body %>