Mergify for v7 branches (#2343)

Author: adamfraser

.github/mergify.yml

@@ -117,4 +117,20 @@ pull_request_rules:
       backport:
         branches:
           - release/protocol/v6.x
+  - name: backport to release/indexer/v7.x branch
+    conditions:
+      - base=main
+      - label=backport/indexer/v7.x
+    actions:
+      backport:
+        branches:
+          - release/indexer/v7.x
+  - name: backport to release/protocol/v7.x branch
+    conditions:
+      - base=main
+      - label=backport/protocol/v7.x
+    actions:
+      backport:
+        branches:
+          - release/protocol/v7.x