What would you like to be added:
Add an option to list all resources in a Shoot namespace on a Seed cluster.

Why is this needed:
A very common issue during operations is that some k8s resources incl. custom resources were leaked within a Shoot namespace on a Seed. Finding them can be hard, so it would be great if gardenctl could integrate a functionality to find them.

Via kubectl it can be done via something like this (simplified):

#!/bin/bash
for res in $(kubectl api-resources --namespaced=true -o=name); do
  kubectl -n <shoot-namespace> get $res
done

It would be great if an operator could trigger this operation for a targeted Shoot cluster directly via gardenctl.

cc @ScheererJ, @mliepold