Implement pod resource metrics as described in KEP 1916. The new
`/metrics/resources` endpoint is exposed on the active scheduler
and reports kube_pod_resources* metrics that present the effective
requests and limits for all resources on the pods as calculated by
the scheduler and kubelet. This allows administrators using the
system to quickly perform resource consumption, reservation, and
pending utilization calculations when those metrics are read.
Because metrics calculation is on-demand, there is no additional
resource consumption incurred by the scheduler unless the endpoint
is scraped.
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