Merge pull request #30638 from krousey/metrics_registration

Automatic merge from submit-queue

Remove implicit Prometheus metrics from client

**What this PR does / why we need it**: This PR starts to cut away at dependencies that the client has.

**Release note**:
<!--  Steps to write your release note:
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```release-note
The implicit registration of Prometheus metrics for request count and latency have been removed, and a plug-able interface was added. If you were using our client libraries in your own binaries and want these metrics, add the following to your imports in the main package: "k8s.io/pkg/client/metrics/prometheus". 
```

cc: @kubernetes/sig-api-machinery @kubernetes/sig-instrumentation @fgrzadkowski  @wojtek-t

contrib/mesos/cmd/km/km.go

@@ -19,6 +19,8 @@ package main
 
 import (
 	"os"
+
+	_ "k8s.io/kubernetes/pkg/client/metrics/prometheus" // for client metric registration
 )
 
 func main() {