metrics: capture pod state change events

[cirocosta]

We've had an event where we've been seeing that a container was apparently being
restarted, but we couldn't easily tell when that started, or whether it was
indeed a restart (or something else).

It'd be great it we could quickly relate to the pod status information right
from the place where we see those metrics (the dashboards we have).

To do so, we could probably leveragge kube-state-metrics:

https://github.com/kubernetes/kube-state-metrics/blob/master/docs/pod-metrics.md

(could probably use kube_pod_status_phase? not sure)