Load refactored Epic app when cookie flag is true

ee/app/assets/javascripts/pages/groups/epics/show/index.js

 import ZenMode from '~/zen_mode';
+import Cookies from 'js-cookie';
 import initEpicShow from 'ee/epics/epic_show/epic_show_bundle';
 import ShortcutsEpic from 'ee/behaviors/shortcuts/shortcuts_epic';
+import initEpicApp from 'ee/epic/epic_bundle';
 import '~/notes/index';
 
 document.addEventListener('DOMContentLoaded', () => {
   new ZenMode(); // eslint-disable-line no-new
-  initEpicShow();
-  new ShortcutsEpic(); // eslint-disable-line no-new
+  if (Cookies.get('load_new_epic_app') === 'true') {
+    initEpicApp();
+  } else {
+    initEpicShow();
+    new ShortcutsEpic(); // eslint-disable-line no-new
+  }
 });

ee/app/views/groups/epics/show.html.haml

@@ -11,7 +11,10 @@
 
 - page_card_attributes @epic.card_attributes
 
-#epic-show-app{ data: epic_show_app_data(@epic, author_icon: avatar_icon_for_user(@epic.author), initial: issuable_initial_data(@epic)) }
+- if cookies[:load_new_epic_app] == 'true'
+  #epic-app-root{ data: epic_show_app_data(@epic, author_icon: avatar_icon_for_user(@epic.author), initial: issuable_initial_data(@epic)) }
+- else
+  #epic-show-app{ data: epic_show_app_data(@epic, author_icon: avatar_icon_for_user(@epic.author), initial: issuable_initial_data(@epic)) }
 
 .content-block.emoji-block
   .row