Migrate from Vue event hub to Mitt in issuables list

app/assets/javascripts/issuables_list/eventhub.js

-import Vue from 'vue';
+import createEventHub from '~/helpers/event_hub_factory';
 
-const issueablesEventBus = new Vue();
-
-export default issueablesEventBus;
+export default createEventHub();

changelogs/unreleased/chore-mitt-migration-issuables-list.yml

+---
+title: Migrate from Vue event hub to Mitt in issuables list
+merge_request: 31652
+author: Arun Kumar Mohan
+type: changed