Instead of using direct CDN how to put the plug-in in an assets folder?

This my not be a bug or issue but a question.

The upload folder contains the plugins for datatables and other plugins, I would like to have an assets folder below app directory to put there others plugins, but when I try to reference it it won't work.

I would like to have something like this:
<script src="<?= base_url();?>/assets/plugins/datatables/jquery.dataTables.min.js"></script>
