DialogBase/DialogEntityDelete: improve Error Handling if delete fails

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](https://github.com/ecamp/ecamp3/assets/1506818/6b8b3393-7bd7-468a-8dfe-5b7f087b0aa2)

_Originally posted by @BacLuc in https://github.com/ecamp/ecamp3/pull/4362#discussion_r1439276175_

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.