NULL character on k8s zone labels

[luisdavim]

A related issue was opened some time ago kubernetes/kubernetes#73867

This https://github.com/kubernetes/kubernetes/blob/master/staging/src/k8s.io/component-helpers/node/topology/helpers.go#L57 adds the NULL character and then because in prometheus %q is used to print the value https://github.com/prometheus/common/blob/main/model/metric.go#L62 the character is printed.

If it makes sense to you I can open a PR to strip these characters from the label values.