Reapply "Modernize codegen in hack/update-codegen.sh"

[bowei]

This reverts commit 5afb60b.

[swetharepakula]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bowei, swetharepakula

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[bowei]

/test

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@bowei: The /test command needs one or more targets.
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[bowei]

/test pull-ingress-gce-verify

[k8s-ci-robot]

New changes are detected. LGTM label has been removed.

[k8s-ci-robot]

@bowei: 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-ingress-gce-verify	381492c	link	true	/test pull-ingress-gce-verify

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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