Update Prometheus documentation to indicate on by default

doc/administration/monitoring/prometheus/gitlab_metrics.md

@@ -17,10 +17,7 @@ GitLab monitors its own internal service metrics, and makes them available at th
 `/-/metrics` endpoint. Unlike other [Prometheus] exporters, in order to access
 it, the client IP needs to be [included in a whitelist][whitelist].
 
-Currently the embedded Prometheus server is not automatically configured to
-collect metrics from this endpoint. We recommend setting up another Prometheus
-server, because the embedded server configuration is overwritten once every
-[reconfigure of GitLab][reconfigure]. In the future this will not be required.
+For Omnibus and Chart installations, these metrics are automatically enabled and collected as of [GitLab 9.4](https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests/1702). For source installations or earlier verisons, these metrics will need to be enabled manually and collected by a Prometheus server.
 
 ## Unicorn Metrics available