Initialize Integrations table for admins on FOSS

This fixes a bug where the integrations
table was not available for FOSS admins.

Also, remove DOMContentLoaded callback

Changelog: fixed

app/assets/javascripts/pages/admin/application_settings/integrations/index.js

+import initIntegrationsList from '~/integrations/index';
 import PersistentUserCallout from '~/persistent_user_callout';
 
-document.addEventListener('DOMContentLoaded', () => {
-  const callout = document.querySelector('.js-admin-integrations-moved');
-  PersistentUserCallout.factory(callout);
-});
+const callout = document.querySelector('.js-admin-integrations-moved');
+
+PersistentUserCallout.factory(callout);
+
+initIntegrationsList();

changelogs/unreleased/fix-admin-integrations-foss.yml

+---
+title: Fix Instance-level Project Integration Management page for GitLab FOSS
+merge_request: 60354
+author:
+type: fixed

spec/features/admin/admin_settings_spec.rb

@@ -305,6 +305,10 @@ RSpec.describe 'Admin updates settings' do
 
         expect(page).not_to have_content('Some settings have moved')
       end
+
+      it 'shows integrations table' do
+        expect(page).to have_selector '[data-testid="inactive-integrations-table"]'
+      end
     end
 
     context 'CI/CD page' do