Refine check for existing serial numbers

In #369 (closed) we have the story to check for existing serial numbers. But currently in the backend there is no way to ignore certain devices to get the set of serial numbers from the database, which resulted in the discussion about the current mechanism to not show the warning when editing an existing device (!398 (comment 3469711)).

In the backend we want to extend the endpoint in order to ignore certain specific devices, so that we can check if another device has the same serial number, even when editing the device: backend#166 (closed)

So the task here is to replace the frontend mechanism to ignore the serial number of the current device by sending the device id as parameter to the backend.