Replace deprecated containrrr/watchtower

[Watchtower ](https://github.com/containrrr/watchtower) is no longer maintained, we need to replace it. We could fork the repository and build our own image. The Dockerfile is https://github.com/containrrr/watchtower/blob/main/dockerfiles/Dockerfile.dev-self-contained Another option is to put the container update into the shabowbox image, so it updates itself. That would require access to the docker socket, with security implications.