[KEP-2400] Add swap memory to the Kubelet stats API

[iholder101]

What would you like to be added?

Add swap memory to the Kubelet stats API so that we have metrics on swap utilization.

• Code changes
• Add e2e coverage

Why is this needed?

https://github.com/kubernetes/enhancements/blob/master/keps/sig-node/2400-node-swap/README.md#beta-1

[k8s-ci-robot]

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[iholder101]

/sig node