Kubeadm stop using v1alpha2 objects

[fabriziopandini]

What this PR does / why we need it:
This PR removes all the references to v1alpha2 objects from kubeadm.

Which issue(s) this PR fixes:
Ref: kubernetes/kubeadm#911

Special notes for your reviewer:
This PR is part of a series or PRs that will remove v1alpha2, cleanup all the references to v1alpha2 objects, and finally add v1beta1 api version; the work is divided into multiple PRs hopefully more easy to review.

Depends on:

• Kubeadm remove v1alpha2 api #69055

Please consider only the last two commits:

• cleanup v1alpha2 from upload/fetch kubeadm config ConfigMap
• remove references to v1alpha2 api kinds

Release note:

NONE

@kubernetes/sig-cluster-lifecycle-pr-reviews
/sig cluster-lifecycle
/kind api-change
/area kubeadm

/cc @timothysc @luxas

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini

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• cmd/kubeadm/OWNERS [fabriziopandini]

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[k8s-ci-robot]

@fabriziopandini: The following tests failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-kubernetes-integration	dc2c251	link	/test pull-kubernetes-integration
pull-kubernetes-verify	dc2c251	link	/test pull-kubernetes-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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[timothysc]

@fabriziopandini - please merge this change with #69055

Closing this issue.