Make current collaborators (grantees) list searchable

## What?

As with various other "lists" in Graylog, it should be possible to search the list of collaborators (grantees) in the entity sharing modal. It would be **very** nice if this also enabled searching on various attributes, since only seeing first name + last name can be problematic (see #10844).

## Why?

When there are a large number of collaborators/grantees it can be tedious to page through the results in the entity sharing modal.

## Your Environment

* Graylog Version: 4.3.2