added pr stack labels from suggest way (#764)

.mergify.yml

@@ -128,14 +128,26 @@ pull_request_rules:
         toggle:
           - "failure: conflict"
   # PR label rules
-  - name: Add PR stack label for stacked PRs
+  - name: Label Mergify Stacks PRs
+    description: Pull requests that are part of a Mergify stack should be labeled as such
     conditions:
-      - -closed
-      - base!=main
+      # Only trigger if the PR is part of a stack
+      - "commits[0].commit_message ~= (?m)Change-Id:"
     actions:
       label:
-        add:
+        toggle:
           - PR stack
+  - name: Label first PR of Mergify Stacks PRs
+    description: The first PR of a Mergify stack should be labeled as such
+    conditions:
+      # Only trigger if the PR is part of a stack
+      - "commits[0].commit_message ~= (?m)Change-Id:"
+      # Ignore PR targeting their children
+      - -base ~= ^mergify_cli/
+    actions:
+      label:
+        toggle:
+          - top of the stack
   - name: toggle generator label
     conditions:
       - -closed