Migrate from k8s.gcr.io to registry.k8s.io

[shikharcodes]

This PR is a part of kubernetes/k8s.io#4780.

Proposed Changes

This PR does the following changes:

• modify all occurrences of k8s.gcr.io to registry.k8s.io.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: shikharcodes / name: Shikhar Saxena (c0e59ae)

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[knative-prow]

Welcome @shikharcodes! It looks like this is your first PR to knative/docs 🎉

[pierDipi]

/lgtm
/approve

[psschwei]

I'm assuming that all images in the old registry are present in the new registry? (Usually I'd check myself, but am not able to do so until next week, if someone could confirm 🙏 )

[dprotaso]

/approve

images can be pulled

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, pierDipi, shikharcodes

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