[en] Replace k8s.gcr.io with registry.k8s.io in blogs

[xmudrii]

This PR replaces k8s.gcr.io with registry.k8s.io in two blog posts where I think it kinda makes sense to do so:

• 2020-01-15-Kubernetes-on-MIPS.md: this blog post talks about what images they built, but both k8s.gcr.io images are available in the registry, so I think updating makes sense
• 2022-12-22-kubelet-credential-providers/index.md: was referencing k8s.gcr.io, I added registry.k8s.io as well

/assign @sftim
xref #39353
xref kubernetes/k8s.io#4738

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[dipesh-rawat]

The registry changes along with added note to explain about the update looks good.

/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: ab68d0258e04799a14a864ac2acffba35e97259e

[reylejano]

/approve

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