Add feature flag to maintaining a pending builds queue

app/services/ci/update_build_queue_service.rb

@@ -14,6 +14,8 @@ module Ci
     # Add a build to the pending builds queue
     #
     def push(build, transition)
+      return unless maintain_pending_builds_queue?
+
       raise InvalidQueueTransition unless transition.to == 'pending'
 
       transition.within_transaction do
@@ -27,6 +29,8 @@ module Ci
     # Remove a build from the pending builds queue
     #
     def pop(build, transition)
+      return unless maintain_pending_builds_queue?
+
       raise InvalidQueueTransition unless transition.from == 'pending'
 
       transition.within_transaction do
@@ -61,5 +65,9 @@ module Ci
         runner.pick_build!(build)
       end
     end
+
+    def maintain_pending_builds_queue?
+      Feature.enabled?(:ci_pending_builds_queue_maintain, default_enabled: :yaml)
+    end
   end
 end

config/feature_flags/development/ci_pending_builds_queue_maintain.yml

+---
+name: ci_pending_builds_queue_maintain
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/61581
+rollout_issue_url: 
+milestone: '13.12'
+type: development
+group: group::continuous integration
+default_enabled: false