Add support for backport command (eclipse-cdt#849)

Fixes eclipse-cdt#842 (comment)

.backportrc.json

@@ -0,0 +1,9 @@
+{
+  "repoOwner": "eclipse-cdt",
+  "repoName": "cdt",
+  "targetBranchChoices": ["tycho-cdt_11_6"],
+  "branchLabelMapping": {
+    "^backport-to-(.+)$": "$1"
+  },
+  "multipleCommits": true
+}

.github/workflows/backport.yml

@@ -0,0 +1,25 @@
+name: Automatic backport action
+
+on:
+  pull_request_target:
+    types: ["labeled", "closed"]
+
+jobs:
+  backport:
+    name: Backport PR
+    runs-on: ubuntu-latest
+    steps:
+      - name: Backport Action
+        uses: sorenlouv/[email protected]
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          auto_backport_label_prefix: backport-to-
+          add_original_reviewers: true
+
+      - name: Info log
+        if: ${{ success() }}
+        run: cat ~/.backport/backport.info.log
+
+      - name: Debug log
+        if: ${{ failure() }}
+        run: cat ~/.backport/backport.debug.log