Instead discard metric values for pods that are unready and have never
been ready (they may report misleading values, the original reason for
introducing scale up forbidden window).

Use per pod metric when pod is:
- Ready, or
- Not ready but creation timestamp and last readiness change are more
  than 10s apart.

In the latter case we asume the pod was ready but later became unready.
We want to use metrics for such pods because sometimes such pods are
unready because they were getting too much load.