Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>..

Collapse all metrics handlers into common code

Remove the MonitorRequest method and replace with a method that takes
request.RequestInfo, which is our default way to talk about API objects.
Preserves existing semantics for calls.

Not for 1.8, but fixes the ugliness and code duplication in #52237