Use user first name or last name when filtering in the rights livetable

The global idea for this issue is similar to XWIKI-21287 : currently, it's only possible to filter users in the rights livetable based on their username, and not their first name / last name. This is usually not an issue if the username is made of some sort of combination of first name + last name, however it becomes more of an issue if the username is a UUID.