User add to Group

I'm always frustrated when adding users to a group in Authentik because the user selection shows ALL users, including those already in the group. This makes it confusing and time-consuming to find users who aren't already members.

When adding users to a group, the user selection should only display users who are NOT currently members of that group.

Adding visual indicators (like grayed-out text) for users already in the group
A separate filter toggle to hide/show existing members

This enhancement would significantly improve UX when managing group memberships, especially for organizations with large user bases.