Skip Pod metrics if any container skipped

[dippynark]

What this PR does / why we need it:

Currently, if a container's start time or CPU seconds decreases, we exclude that container's resource usage from the exposed metrics for its Pod:

metrics-server/pkg/storage/types.go

Lines 54 to 59 in 78192ed

	if last.StartTime.Before(prev.StartTime) {
	return corev1.ResourceList{}, api.TimeInfo{}, fmt.Errorf("unexpected decrease in startTime of node/container")
	}
	if last.CumulativeCPUUsed < prev.CumulativeCPUUsed {
	return corev1.ResourceList{}, api.TimeInfo{}, fmt.Errorf("unexpected decrease in cumulative CPU usage value")
	}

In particular, if a Pod has multiple containers and one of the containers hits this condition, the Pod's metrics are still reported but with that container's contribution excluded. This can look like the Pod's utilisation is significantly lower than it actually is which can be especially problematic when using this information for horizontal or vertical scaling.

This PR changes this behaviour to exclude the entire Pod, favouring accurate metrics over unreliable/inconsistent metrics.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: dippynark
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[k8s-ci-robot]

Hi @dippynark. Thanks for your PR.

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[dippynark]

/assign @RainbowMango

[dgrisonnet]

/ok-to-test

[dgrisonnet]

@dippynark thank you for the contribution. Do you think you could write a test for the scenario you described?

[dgrisonnet]

/triage accepted