Optimisation to access the profil of a user

## Bug Report

**Expected behavior/code**
When we tag a user using the @ mention in a post, a link is created to target the user's profile.
If my user has subscribed to a lot of courses, this query takes many seconds, it needs to be optimized.


**Possible Solution**
limit queries to the LTI Context to filter results, see optimization for the search.

