Add example Grafana dashboard (#981)

* Add example Grafana dashboard

* Update Grafana example dashboard datasource

* Update dashboard name and fix datasource issue

* Fix running state in example Grafana dashboard

Author: kvklink

docs/reference-docs/metrics.md

@@ -35,6 +35,8 @@ wfo_engine_status{wfo_engine_status="RUNNING"} 1.0
 wfo_active_process_count 5.0
 ```
 
+An example Grafana dashboard that uses these metrics is given in the code repository in `grafana-example.json`.
+
 ## Adding custom metrics
 
 It's possible to add more metric collectors to your orchestrator, if there are organisation-specific metrics you want