Move jquery.endless-scroll import away from main

This moves the import of `jquery.endless-scroll` from main to
`app/assets/javascripts/pager.js`

It is the only file that utilizes it and thus we don't need to load it
on every page.

The issue to replace it completely can be found here:
https://gitlab.com/gitlab-org/gitlab/-/issues/219367

app/assets/javascripts/commons/jquery.js

@@ -2,7 +2,6 @@ import 'jquery';
 
 // common jQuery plugins
 import 'jquery-ujs';
-import 'vendor/jquery.endless-scroll';
 import 'jquery.caret'; // must be imported before at.js
 import '@gitlab/at.js';
 import 'vendor/jquery.scrollTo';

app/assets/javascripts/pager.js

 import $ from 'jquery';
+import 'vendor/jquery.endless-scroll';
 import { getParameterByName } from '~/lib/utils/common_utils';
 import axios from '~/lib/utils/axios_utils';
 import { removeParams } from '~/lib/utils/url_utility';