Unify the approach to manage etcd images in Kubernetes

[ahrtr]

What would you like to be added?

The etcd container images are currently built from cluster/images/etcd, pushed to registry.k8s.io/etcd, and used by kubeadm, KOps and Kubernetes workflow tests.

Concerns & comments,

• It would be good to consider moving the image build definition out of the Kubernetes repo
• Why not to use etcd officially released images?

Proposals,

• Push etcd officially released images to registry.k8s.io/etcd
• Deprecate the migration tool

See also https://docs.google.com/document/d/1B0C391PJ2zwHnmIwOWpzq-tjzj9-Gci-Ph2k9mwC5R4/edit?tab=t.0#heading=h.xblvj5c0ffhf

Please feel free to comment on the google doc, thx

cc @ivanvc @jmhbnz @serathius @siyuanfoundation @wenjiaswe @neolit123 @liggitt @BenTheElder @hakman

Why is this needed?

to ensure a smooth switch to etcd offically released images