Added backport workflow.

Author: StefanFabian

.github/workflows/backport.yaml

@@ -0,0 +1,18 @@
+name: Backport
+on:
+  pull_request_target:
+    types: [closed, labeled]
+permissions:
+  contents: write
+  pull-requests: write
+jobs:
+  backport:
+    name: Backport
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.merged == true
+    steps:
+      - uses: actions/checkout@v6.0.2
+      - name: Create backport pull request
+        uses: korthout/backport-action@v4.3.0
+        with:
+          github_token: '${{ secrets.BACKPORT_PAT }}'