If the user runs "kubeadm upgrade apply", kubeadm can download
a configuration from the cluster. If the configuration contains
the legacy default imageRepository of "k8s.gcr.io", mutate it
to the new default of "registry.k8s.io" and update the
configuration in the config map.
During "upgrade node/diff" download the configuration, mutate the
image repository locally, but do not mutate the in-cluster value.
That is done only on "apply".
This ensures that users are migrated from the old default registry
domain.
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