Automatic merge from submit-queue (batch tested with PRs 45382, 45384, 44781, 45333, 45543)

Copy internal types to metrics

Supersedes #45306. 

#45306 removed the internal types and suggested whoever needs the internal types should define their own copy, and use the code-gen tools to generated the conversion functions. Per offline discussion with @DirectXMan12, we wanted to go that direction but it's not clear where to put the internal types yet. Hence, as a temporary solution, we decided copy the referred client-go/pkg/api types into metrics api to avoid the dependency.

The commit "remove need of registry from custom_metrics/client.go" is similar to what I did to the fake client in an earlier PR. Let me know if you want to put the commit in another PR.