Resolve "Change the order of project/group members in assignees widget"

What does this MR do and why?

This MR applies the correct sorting of the project members on the assignees widget. Previously, they were sorted by created date and we couldn't pass a parameter to the GraphQL query to change this order. Now, we pass the sort parameter to sort users in alphabetical order by their full names.

Additionally, this MR fixes a small bug wit positioning cannot-merge icon on the user avatar

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Enable the assignees widget feature flag

   Feature.enable(:issue_assignees_widget)

2. Open any merge request.
3. On the sidebar, open assignees dropdown.
4. The order of the users should be the following: assigned users, current user (if not assigned), MR author (if not assignees), project members in alphabetical order.
5. "Cannot merge" icon should be placed in the bottom right corner of the user avatar.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #355974 (closed)