Add missing circuitbreaker metrics to prometheus documentation

doc/administration/monitoring/prometheus/gitlab_metrics.md

@@ -20,7 +20,7 @@ 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. 
+[reconfigure of GitLab][reconfigure]. In the future this will not be required.
 
 ## Metrics available
 
@@ -45,6 +45,8 @@ In this experimental phase, only a few metrics are available:
 | redis_ping_success                | Gauge     | 9.4   | Whether or not the last redis ping succeeded |
 | redis_ping_latency_seconds        | Gauge     | 9.4   | Round trip time of the redis ping |
 | user_session_logins_total         | Counter   | 9.4   | Counter of how many users have logged in |
+| filesystem_circuitbreaker_latency_seconds | Histogram | 9.5 | Latency of the stat check the circuitbreaker uses to probe a shard |
+| filesystem_circuitbreaker         | Gauge     | 9.5   | Wether or not the circuit for a certain shard is broken or not |
 
 ## Metrics shared directory