Automatic merge from submit-queue (batch tested with PRs 45077, 45180, 34727, 45079, 45177)

Move k8s.io/metrics to staging/

This is to break the cyclic dependency in our code base: kubernetes depends on k8s.io/metrics, which depends on kubernetes/staging/client-go.

@DirectXMan12 i actually moved it to staging because we will need the flexibility to update metrics code directly to do many planned refactors, so the copy of metrics in kubernetes has to be the source of truth.

client-gen is not enabled for the code yet, we can enable it after you port your changes to client-gen.

`make generated_files` is enabled for metrics.