[Release] add-backport-next (#51809) (#51825)

(cherry picked from commit cc3b0a6)

Co-authored-by: elastic-vault-github-plugin-prod[bot] <150874479+elastic-vault-github-plugin-prod[bot]@users.noreply.github.com>
Co-authored-by: elasticmachine <infra-root+elasticmachine@elastic.co>

Author: 3 people

.mergify.yml

@@ -357,3 +357,11 @@ pull_request_rules:
       backport:
         branches:
           - "9.4"
+  - name: backport patches to 9.5 branch
+    conditions:
+      - merged
+      - label=backport-9.5
+    actions:
+      backport:
+        branches:
+          - "9.5"