kubelet: fix pod ready state flips after kubelet restart

[x-zl]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Currently, after kubelet restart, if a pod has readiness probe, the ready state will flip:
Ready pod: ready --> not ready --> ready
Not ready pod: not ready --> ready --> not ready

Which issue(s) this PR is related to:

Fixes #131303

Special notes for your reviewer:

Root Cause:
In the probeManager.UpdatePodStatus function, pods that don't have readiness workers found will have their ready status set to true by default. However, during kubelet restart, when this function is called, kubelet hasn't yet added this pod's readiness to the probeManager's workers, so not-ready pods will briefly become ready until the next probe completes.

Meanwhile, when probeManager calls the newWorker function, readiness.initialValue is constantly set to Failure, which causes originally ready pods to briefly change from ready to not-ready until the next probe completes.

Does this PR introduce a user-facing change?

NONE

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

[k8s-ci-robot]

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[k8s-ci-robot]

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[k8s-ci-robot]

Hi @x-zl. Thanks for your PR.

I'm waiting for a kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: x-zl
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[toVersus]

/hold

@HirazawaUi is already working on fixing this issue and has created a KEP. It would be redundant effort, so I think it’s better to review the KEP and provide feedback if you have any concerns.

KEP: kubernetes/enhancements#5493
PoC: #133676

[HirazawaUi]

Yes, fixing this issue is not particularly complex, and there are multiple approaches to resolve it. However, it might break some of our existing use cases, so extra caution is needed when addressing it, along with further discussion. If you would like to help advance this issue toward a resolution, feel free to share your opions on kubernetes/enhancements#5493.

[k8s-ci-robot]

PR needs rebase.

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