User search should match on first character entered when adding approvers to merge request

ZD Ticket: https://gitlab.zendesk.com/agent/tickets/83759

Summary

When adding approvers to a merge request, a list of possible approvers is shown when you click in the search box. However, as soon as you start typing to search for a user the list disappears and "No matches found" is shown. Possible matches are only shown again once you've entered at least 3 characters. This gives users the impression that there are no search results.

Steps to reproduce

Probably other ways to do this, but here are the steps I followed:

1. Enable merge request approvals on your project
2. Require 2 approvers but dont set any approvers
3. Create a merge request
4. Click in the "Approvers" search box and see a dropdown list of possible approvers is shown
5. Enter 1 or 2 characters to search for a user(s) and the list is replaced with "No matches found"
6. Enter a 3rd character and matches are shown

What is the current bug behavior?

Users are only matched when 3 or more characters are entered.

What is the expected correct behavior?

Users should be matched from the 1st character entered.

Relevant logs and/or screenshots