Promote size memory backed volumes to beta

[derekwaynecarr]

Documentation update for KEP:
kubernetes/enhancements#2345

Alpha documentation had no behavior change.

[k8sio-netlify-preview-bot]

Deploy preview for kubernetes-io-vnext-staging processing.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[derekwaynecarr]

/hold

waiting to hear from release team on exception:
https://groups.google.com/g/kubernetes-sig-node/c/7w1vqksOqHY

[irvifa]

Since the exception was denied what should we do with this PR?

[reylejano]

Closing the PR since the exception was denied
https://groups.google.com/g/kubernetes-sig-node/c/7w1vqksOqHY

If the enhancement will be tracked for 1.22, this PR can be re-opened and target the dev-1.22 branch once the branch is created

/close

[k8s-ci-robot]

@reylejano: Closed this PR.

In response to this:

Closing the PR since the exception was denied
https://groups.google.com/g/kubernetes-sig-node/c/7w1vqksOqHY

If the enhancement will be tracked for 1.22, this PR can be re-opened and target the dev-1.22 branch once the branch is created

/close

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