add upgrade script for kubeadm

[neolit123]

Add the script kubeadm/KubeClusterUpgrade.ps1 that handles
upgrades of Windows worker nodes created by kubeadm.

It does the following:

• Downloads new binaries.
• Calls "kubeadm upgrade node".
• Restarts kube-proxy and kubelet services.

Currently it does not:

• Update CNI as the version matrix there is unclear.
• Drain a worker as this is the responsibility of the cluster admin
  (owner of admin.conf).

NOTE: i did not add this as part of KubeCluster.ps1 as the script is quite broken for me.
possibly my PowerShell version is too old or something.

xref
#24

[neolit123]

/kind feature
/priority important-longterm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[neolit123]

closing in favor of documentation, see:
kubernetes/website#19217
#24 (comment)

/close

[k8s-ci-robot]

@neolit123: Closed this PR.

In response to this:

closing in favor of documentation, see:
kubernetes/website#19217
#24 (comment)

/close

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