feature: availability zone from node label?

[ancoron]

As officially documented, we can label a node to tell in which availability zone it is:

• https://kubernetes.io/docs/reference/labels-annotations-taints/#topologykubernetesiozone

So, as a result, the label topology.kubernetes.io/zone can be used as a fallback mechanism in Kubernetes environments to detect the zone in cases where no cloud node info is available.

For on-prem environments, the label to look for could also be made configurable. This way, what is classified as a "zone" also becomes a bit more flexible.