Consider using informers to watch k8s resources rather than listing

[cbroglie]

The client-go informers package provides utilities to subscribe to changes to k8s resources and keep an in-memory cache up to date. This avoids needing to ask the API server to fetch the list from etcd every refresh interval, and allows probes to always operate on fresh data.

If there's interest, I'd be happy to submit a PR with the necessary changes.