Add feature flag for toggling vue sidebar

app/controllers/projects/issues_controller.rb

@@ -42,6 +42,10 @@ class Projects::IssuesController < Projects::ApplicationController
   before_action :authorize_import_issues!, only: [:import_csv]
   before_action :authorize_download_code!, only: [:related_branches]
 
+  before_action do
+    push_frontend_feature_flag(:vue_issuable_sidebar, project.group)
+  end
+
   respond_to :html
 
   alias_method :designs, :show

app/controllers/projects/merge_requests_controller.rb

@@ -21,6 +21,10 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     push_frontend_feature_flag(:diffs_batch_load, @project)
   end
 
+  before_action do
+    push_frontend_feature_flag(:vue_issuable_sidebar, @project.group)
+  end
+
   around_action :allow_gitaly_ref_name_caching, only: [:index, :show, :discussions]
 
   def index

ee/app/controllers/groups/epics_controller.rb

@@ -18,6 +18,7 @@ class Groups::EpicsController < Groups::ApplicationController
   before_action do
     push_frontend_feature_flag(:epic_trees, @group)
     push_frontend_feature_flag(:roadmap_graphql, @group)
+    push_frontend_feature_flag(:vue_issuable_epic_sidebar, @group)
   end
 
   def index