KEP-3705 CloudDualStackNodeIPs to GA

[danwinship]

What this PR does / why we need it:

Moves KEP-3705 CloudDualStackNodeIPs to GA, as per kubernetes/enhancements#4415

Special notes for your reviewer:

I removed the allowCloudDualStack argument from ParseNodeIPArgument (since it would always be true now) but left the cloudProvider argument since kubelet still has some code for the legacy providers?

Does this PR introduce a user-facing change?

Graduated support for passing dual-stack `kubelet --node-ip` values when using
a cloud provider. The feature is now GA and the `CloudDualStackNodeIPs` feature
gate is always enabled.

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

- [KEP]: https://github.com/kubernetes/enhancements/issues/3705

/kind feature
/priority important-soon
/assign @thockin

[danwinship]

/retest

[thockin]

Thanks!

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 28a9a5fc988e87999ceb8bb260231567be8f7da9

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: danwinship, thockin

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Needs approval from an approver in each of these files:

• cmd/kubelet/OWNERS [thockin]
• pkg/features/OWNERS [danwinship,thockin]
• staging/src/k8s.io/cloud-provider/OWNERS [thockin]
• staging/src/k8s.io/component-helpers/node/OWNERS [thockin]
• staging/src/k8s.io/controller-manager/pkg/features/OWNERS [danwinship,thockin]

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/retest

[seans3]

/triage accepted

[sftim]

Changelog suggestion

-The CloudDualStackNodeIPs feature is now GA and the feature gate is always
-enabled, meaning that dual-stack `kubelet --node-ip` values are always supported
+Graduated dual-stack support for kubelet cloud provider integrations.
+The feature is now GA and the `CloudDualStackNodeIPs`  feature gate is always
+enabled, meaning that dual-stack `kubelet --node-ip` values are always supported
 (when using an external cloud provider that supports dual stack). 

[danwinship]

+Graduated dual-stack support for kubelet cloud provider integrations.

That makes it sound bigger than it is... how about

Graduated support for passing dual-stack `kubelet --node-ip` values when using
a cloud provider. The feature is now GA and the `CloudDualStackNodeIPs`  feature
gate is always enabled.

?