mergify: support backport-active-8, backport-active-9, backport-active-all (#2989)

* mergify: support backport-active-8, backport-active-9, backport-active-all

* nit

Author: v1v

.mergify.yml

@@ -131,6 +131,9 @@ pull_request_rules:
           To fixup this pull request, you need to add the backport labels for the needed
           branches, such as:
           * `backport-v./d./d./d` is the label to automatically backport to the `8./d` branch. `/d` is the digit
+          * `backport-active-all` is the label that automatically backports to all active branches.
+          * `backport-active-8` is the label that automatically backports to all active minor branches for the 8 major.
+          * `backport-active-9` is the label that automatically backports to all active minor branches for the 9 major.
           **NOTE**: `backport-v8.x` has been added to help with the transition to the new branch 8.x.
       label:
         add:
@@ -378,3 +381,56 @@ pull_request_rules:
         labels:
           - "backport"
         title: "[{{ destination_branch }}](backport #{{ number }}) {{ title }}"
+
+  - name: backport patches to all active minor branches for the 8 major.
+    conditions:
+      - merged
+      - label=backport-active-8
+    actions:
+      backport:
+        assignees:
+          - "{{ author }}"
+        # NOTE: this list needs to be changed when a new minor branch is created
+        #       or an existing minor branch reached EOL.
+        branches:
+          - "8.18"
+          - "8.17"
+          - "8.16"
+        labels:
+          - "backport"
+        title: "[{{ destination_branch }}](backport #{{ number }}) {{ title }}"
+  - name: backport patches to all active minor branches for the 9 major.
+    conditions:
+      - merged
+      - label=backport-active-9
+    actions:
+      backport:
+        assignees:
+          - "{{ author }}"
+        # NOTE: this list needs to be changed when a new minor branch is created
+        #       or an existing minor branch reached EOL.
+        branches:
+          - "9.0"
+        labels:
+          - "backport"
+        title: "[{{ destination_branch }}](backport #{{ number }}) {{ title }}"
+  - name: backport patches to all active branches
+    conditions:
+      - merged
+      - label=backport-active-all
+    actions:
+      backport:
+        assignees:
+          - "{{ author }}"
+        # NOTE: this list needs to be changed when a new minor branch is created
+        #       or an existing release branch reached EOL.
+        branches:
+          - "9.0"
+          - "8.18"
+          - "8.17"
+          - "8.16"
+          - "8.x"
+          - "7.17"
+        labels:
+          - "backport"
+        title: "[{{ destination_branch }}](backport #{{ number }}) {{ title }}"