Locked files: not enough infos for end user, too much for admin

⚠️ This issue respects the following points: ⚠️ • This is a bug, not a question or a configuration/webserver/proxy issue. • This issue is not already reported on [Github]( OR [Nextcloud Community Forum]( _(I've searched it)_. • Nextcloud Server is up to date. See [Maintenance and Release Schedule]( for supported versions. • I agree to follow Nextcloud's [Code of Conduct]( Bug description When someone tries to move/delete/edit a locked file, he/she gets an incomplete notification while admin get errors as if something were abnormal. Steps to reproduce 1. try to delete a locked file 2. see the error popup "action failed: deleting file" (or something like that, my interface is in french) 3. go to the logs and see the Locked Exception thrown: Sabre\DAV\Exception\Locked error Expected behavior • End user should see a complete warning : "action failed: file is locked by [...]" (and it could be a simple warning like "th…