k8s: add metric for pod status conditions

[gdvalle]

Area(s)

area:k8s

Is your change request related to a problem? Please describe.

open-telemetry/opentelemetry-collector-contrib#32941

I would like to be able to see a pod's Ready status in metrics.

Describe the solution you'd like

I would like all pod status conditions to be represented in a metric to cover the Pod Ready case, among others.

For example, k8s.pod.status.condition.

Describe alternatives you've considered

An explicit k8s.pod.ready metric, that would go along side k8s.container.ready. I feel this is a half-measure, and we'll only end up wanting to support other conditions, some of which will be custom (not part of k8s core). It seems better if we can map closer to k8s pod spec and present these in the same way.

Additional context

open-telemetry/opentelemetry-collector-contrib#32941 (comment) has a concrete example of this.