new-pod-scale-up-delay=0 should effectively disable filtering out young pods

[jakubin]

What type of PR is this?

/kind feature

What this PR does / why we need it:

StaticAutoscaler.filterOutYoungPods calculates pod age based on CA loop start time. Technically, this means that even with flag --new-pod-scale-up-delay=0s, CA might skip pods that were created between CA loop start and when pods where listed. --new-pod-scale-up-delay=0s should mean that filtering out young pods is disabled.

This is quite an edge case for normal pods, but we'd like to set the creation date for fake pods injected by CapacityBuffer to be able to measure how fast CapacityBuffer pods are processed. Without this PR, cluster autoscaler would filter out those fake pods on the first loop execution, delaying the capacity buffers processing.

Which issue(s) this PR fixes:

No issue

Special notes for your reviewer:

This was tested with with CA started locally running against GKE cluster with all autoscaling disabled:

1. When --new-pod-scale-up-delay was not set (defaulted to 0s), CA immediately triggered MIG scale up
2. With --new-pod-scale-up-delay=1m, the scale up happened after ~1m. Logs:

Initially:
I0102 15:08:41.234214 1598444 static_autoscaler.go:990] Pod ca-test-deployment-9d89c59d-vtsfm is 4.456 seconds old, too new to consider unschedulable

After 1m:
I0102 15:09:37.055125 1598444 klogx.go:87] Pod default/ca-test-deployment-9d89c59d-r96dp is unschedulable

Does this PR introduce a user-facing change?

With `--new-pod-scale-up-delay=0s` (or default value), pods created after CA loop start (i.e. with "negative" age) will not be filtered out.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: jakubin
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