use k8s-staging-images vs kubernetes-ci-images

[spiffxp]

Related:

• This is part of: Deprecate and migrate away from gs://kubernetes-release-dev and gcr.io/kubernetes-ci-images kubernetes/k8s.io#2318
• Similar PR: 📖 use k8s-staging-ci-images vs kubernetes-ci-images kubernetes-retired/cluster-api-bootstrap-provider-kubeadm#300
• The change this is documenting, which landed 2021-01-14: kubeadm: change the default image repository for CI images from gcr.io/kubernetes-ci-images to gcr.io/k8s-staging-ci-images kubernetes/kubernetes#97087

I did this as a straight search-replace because it was unclear to me how exactly the files I changed are used.

I had initially tried using genref but it excluded v1beta1, and pulled in way more stuff, which is the sort of thing I'd expect a regular contributor to this repo to handle.

[spiffxp]

/cc @tengqm @neolit123

[neolit123]

/lgtm
this was changed in k/k here:
kubernetes/kubernetes@d067c2e

[tengqm]

This is fine.
/approve

[k8s-ci-robot]

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