[ci] Disable some workflow use github app instead to have stable performance. (#18132)

Why I did it
github workflow is not easy to extend to other repos.
Use github app instead to share the same workflow.

Work item tracking
Microsoft ADO (number only): 26855292
How I did it
How to verify it

Author: liushilongbuaa

.github/workflows/automerge_scan.yml

@@ -6,7 +6,8 @@ on:
 
 jobs:
   automerge_scan:
-    if: github.repository_owner == 'sonic-net'
+    # Disable workflow, and use pipeline instead to have same logic with other automation
+    if: github.repository_owner == 'sonic-net' && false
     runs-on: ubuntu-latest
     steps:
     - name: Debug

.github/workflows/pr_cherrypick_poststep.yml

@@ -8,7 +8,8 @@ on:
 
 jobs:
   post_cherry_pick:
-    if: github.event.pull_request.merged == true && contains(github.event.pull_request.labels.*.name, 'automerge') && github.event.pull_request.head.user.login == 'mssonicbld' && startsWith(github.event.pull_request.title, '[action]')
+    # Use azpw instead to have stable performance
+    if: false && github.event.pull_request.merged == true && contains(github.event.pull_request.labels.*.name, 'automerge') && github.event.pull_request.head.user.login == 'mssonicbld' && startsWith(github.event.pull_request.title, '[action]')
     runs-on: ubuntu-latest
     steps:
     - name: Debug

.github/workflows/pr_cherrypick_prestep.yml

@@ -9,7 +9,8 @@ on:
 
 jobs:
   pre_cherry_pick:
-    if: github.repository_owner == 'sonic-net' && github.event.pull_request.merged == true && ( (github.event.action == 'closed' && contains(join(github.event.pull_request.labels.*.name, ','), 'Approved for 20')) || (github.event.action == 'labeled' && startsWith(github.event.label.name, 'Approved for 20')) )
+    # Use azpw instead of workflow to have stable performance.
+    if: false && github.repository_owner == 'sonic-net' && github.event.pull_request.merged == true && ( (github.event.action == 'closed' && contains(join(github.event.pull_request.labels.*.name, ','), 'Approved for 20')) || (github.event.action == 'labeled' && startsWith(github.event.label.name, 'Approved for 20')) )
     runs-on: ubuntu-latest
     steps:
     - name: Checkout