Get attribute-based access control info into docs

> At the end of the file there's a section about attribute-based access control that ends with:
>
> > For more information, see [Document-level attribute-based access control with X-Pack 6.1](https://www.elastic.co/blog/attribute-based-access-control-with-xpack).
>
> I don't know if linking to such an old blog post is a good idea if we now have a lot of docs about Document Level Security... for example we could link to wherever this page is mapped: https://www.elastic.co/guide/en/elasticsearch/reference/current/es-dls-overview.html

_Originally posted by @eedugon in https://github.com/elastic/docs-content/pull/340#discussion_r1958756493_

Actual page impacted is https://www.elastic.co/docs/deploy-manage/users-roles/cluster-or-deployment-auth/user-roles