Update metrics.md - centralize the info in the discussion

Author: camilamacedo86

docs/book/src/reference/metrics.md

@@ -21,7 +21,6 @@ enabled by default via Controller-Runtime's feature [WithAuthenticationAndAuthor
 If you want to continue using [kube-rbac-proxy](https://github.com/brancz/kube-rbac-proxy) then you MUST change
 your project to use the image from another source.
 
-> This infrastructure is outside of our control, we cannot guarantee any timeline or any extensions.
 > For further information, see: [kubebuilder/discussions/3907](https://github.com/kubernetes-sigs/kubebuilder/discussions/3907)
 
 </aside>
@@ -327,4 +326,4 @@ In order to publish metrics and view them on the Prometheus UI, the Prometheus i
 Those metrics will be available for prometheus or
 other openmetrics systems to scrape.
 
-![Screen Shot 2021-06-14 at 10 15 59 AM](https://user-images.githubusercontent.com/37827279/121932262-8843cd80-ccf9-11eb-9c8e-98d0eda80169.png)
+![Screen Shot 2021-06-14 at 10 15 59 AM](https://user-images.githubusercontent.com/37827279/121932262-8843cd80-ccf9-11eb-9c8e-98d0eda80169.png)