docs: Grafana dashboard link added to metrics.md (#5165)

Signed-off-by: Alexandre <alexandre@insideboard.com>

docs/metrics.md

@@ -148,6 +148,10 @@ over time, we are no longer interested in the previous metric and can assume it
 In summary, whenever you want to track a particular metric over time, you should use the same metric name _and_ metric
 labels wherever it is emitted. This is how these metrics are "linked" as belonging to the same series.
 
+### Grafana Dashboard for Argo Controller Metrics
+
+Please see the [Argo Workflows metrics](https://grafana.com/grafana/dashboards/13927) Grafana dashboard.
+
 ## Defining metrics
 
 Metrics are defined in-place on the Workflow/Step/Task where they are emitted from. Metrics are always processed _after_
@@ -287,3 +291,4 @@ To define a realtime metric simply add `realtime: true` to a gauge metric with a
     realtime: true
     value: "{{duration}}"
 ```
+