fix cold start time increase issue

[kinderyj]

Fixes #15477

Proposed Changes

• For Kubernetes clusters without mesh enabled, it's preferable to probe the pod directly. However, if podsAddressable is set to false, the activator will continuously probe the cluster, leading to significantly longer cold start times. To re-enable pod probing, you must restart the activator pod. This is because the podsAddressable setting resets to its default value of true only during the activator's startup and initialization.

Release Note

Fix cold start time increase issue.

[linux-foundation-easycla]

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• ✅ login: kinderyj / name: Matt Wang (bd35675)

[knative-prow]

Welcome @kinderyj! It looks like this is your first PR to knative/serving 🎉

[knative-prow]

Hi @kinderyj. Thanks for your PR.

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[knative-prow]

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[skonto]

@ReToCode thoughts on this one?

[ReToCode]

Hm, I'm not sure about all the implications here. Last time I did dig down that rabbithole, this flag had more effects than just that.

Also, instead of setting this, probably Activator should rather watch that config and reconfigure instead of needing the restart.