chore: configure mergify

.github/mergify.yml

@@ -0,0 +1,24 @@
+defaults:
+  actions:
+    backport:
+      # By default, all backport PRs are assigned to the original author.
+      assignees:
+        - "{{ author }}"
+
+pull_request_rules:
+  - name: backport patches to v3.0.x branch
+    conditions:
+      - base=main
+      - label=backport/v3.0.x
+    actions:
+      backport:
+        branches:
+          - release/v3.0.x
+  - name: backport patches to v4.0.x branch
+    conditions:
+      - base=main
+      - label=backport/v4.0.x
+    actions:
+      backport:
+        branches:
+          - release/v4.0.x