Merge branch 'dg-fix-assignees-widget-issues' into 'master'

Use autocomplete query in assignees widget to avoid duplicates

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145370



Merged-by: Natalia Tepluhina <ntepluhina@gitlab.com>
Approved-by: Nick Leonard <nleonard@gitlab.com>
Approved-by: Rajan Mistry <rmistry@gitlab.com>
Approved-by: Natalia Tepluhina <ntepluhina@gitlab.com>
Reviewed-by: Nick Leonard <nleonard@gitlab.com>
Reviewed-by: Rajan Mistry <rmistry@gitlab.com>
Co-authored-by: Deepika Guliani <dguliani@gitlab.com>