mergify: use GitHub checks and add backports (#3805)

Author: v1v

.mergify.yml

@@ -1,7 +1,7 @@
 queue_rules:
   - name: default
     conditions:
-      - check-success=beats-ci/e2e-testing/pr-merge
+      - "check-success=Run Test"
 
 pull_request_rules:
   - name: ask to resolve conflict
@@ -206,3 +206,29 @@ pull_request_rules:
         labels:
           - "backport"
         title: "[{{ destination_branch }}](backport #{{ number }}) {{ title }}"
+  - name: backport patches to 8.12 branch
+    conditions:
+      - merged
+      - label=backport-v8.12.0
+    actions:
+      backport:
+        assignees:
+          - "{{ author }}"
+        branches:
+          - "8.12"
+        labels:
+          - "backport"
+        title: "[{{ destination_branch }}](backport #{{ number }}) {{ title }}"
+  - name: backport patches to 8.13 branch
+    conditions:
+      - merged
+      - label=backport-v8.13.0
+    actions:
+      backport:
+        assignees:
+          - "{{ author }}"
+        branches:
+          - "8.13"
+        labels:
+          - "backport"
+        title: "[{{ destination_branch }}](backport #{{ number }}) {{ title }}"