Automated cherry pick of #12966: add instance connection draining for NLBs

[heybronson]

Cherry pick of #12966 on release-1.23.

#12966: add instance connection draining for NLBs

For details on the cherry pick process, see the cherry pick requests page.

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[k8s-ci-robot]

@heybronson: The following tests 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-verify-govet	bd775ce	link	true	/test pull-kops-verify-govet
pull-kops-verify-generated	bd775ce	link	true	/test pull-kops-verify-generated

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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