Use kcp-dev/code-generator for informers/listers

[fabianvf]

TODO:

• handle the removal of the changes to informer/lister gen in a better way than just checking the file out
• Make hack/update-kcp-codegen.sh work. For now using hack/update-kcp-codegen-orig.sh which doesn't use the kube bash libraries (and therefore doesn't use the variables for getting all the group versions for generation). That should be removed before this merges