Use protobuf

[serathius]

Experimenting with fixing kops validate cluster --wait not working for large cluster #18065

First rule of K8s, always use protobuf

[k8s-ci-robot]

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[k8s-ci-robot]

@serathius: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kops-e2e-k8s-aws-amazonvpc	d3232c3	link	true	/test pull-kops-e2e-k8s-aws-amazonvpc

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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