In the case permissions has been added on dashboard(s). Later permissions for the
parent folder of the dashboard is edited in such a way that dashboard in that folder
has a permission that is a duplicate of an inherited one. This PR changes so that
duplicate permissions are now filtered out from /api/dashboards/id/<dashboard id>/permissions.
Duplicate permission are not filtered out if the permission on dashboard is higher
than on the inherited folder.
Fixes#33296
Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>