DialogBase/DialogEntityDelete: improve Error Handling if delete fails

[BacLuc]

If the Entity to Delete does not exist anymore (we get 404), we now see at least the error for a short time.
But because the entity to delete does not exist, we cannot really go back.

Screencast.from.02.01.2024.10.27.18.webm

Originally posted by @BacLuc in #4362 (comment)

Error cases which need to be considered

• 401: The authorization expired
• 403: you are not allowed to delete this entity
• Network Error: the request did not get through
• 500: Something on the server side failed.