Add pod-startup liveness-probe holdoff for slow-starting pods

[matthyx]

Enhancement Description

• One-line enhancement description (can be used as a release note): adds initializationFailureThreshold to probes allowing a greater number of failures during the initial start of the container.
• Kubernetes Enhancement Proposal: 20190221-livenessprobe-holdoff
• Primary contact (assignee): @matthyx
• Responsible SIGs: @kubernetes/sig-node-api-reviews
• Enhancement target (which target equals to which milestone):
  • Alpha release target (x.y) v1.16
  • Beta release target (x.y) v1.18
  • Stable release target (x.y) v1.20
• Documentation PR: Promote startupProbe to GA in 1.20 website#23332

[matthyx]

/sig node

[matthyx]

/assign @derekwaynecarr

[matthyx]

/kind api-change

[matthyx]

/milestone v1.15

[k8s-ci-robot]

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In response to this:

/milestone v1.15

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[matthyx]

/stage alpha

[matthyx]

@kacole2 the feature is implemented in this PR: kubernetes/kubernetes#71449