Add `:vue_epics_list` feature flag

config/feature_flags/development/vue_epics_list.yml

+---
+name: vue_epics_list
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/46769
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/276189
+milestone: '13.9'
+type: development
+group: group::product planning
+default_enabled: false

ee/app/controllers/groups/epics_controller.rb

@@ -18,6 +18,10 @@ class Groups::EpicsController < Groups::ApplicationController
   before_action :verify_group_bulk_edit_enabled!, only: [:bulk_update]
   after_action :log_epic_show, only: :show
 
+  before_action do
+    push_frontend_feature_flag(:vue_epics_list, @group, type: :development, default_enabled: :yaml)
+  end
+
   feature_category :epics
 
   def new