Solr still uses a lot of field related RAM

Similarly to XWIKI-22820, we noticed that quite a lot of RAM was dedicated data about the field "title_sort" (of type "lowercase").

I notice than in recent version Solr decided to enable docValues by default, and it's now applied to all the types of the default core (except for the "ignored" one). I think we should follow the same logic to avoid keeping having the same problem.