feat: expose prometheus port in helm chart (#10448)

Co-authored-by: Dean Sheather <dean@deansheather.com>

docs/admin/prometheus.md

@@ -35,7 +35,8 @@ The Prometheus endpoint can be enabled in the
 [Helm chart's](https://github.com/coder/coder/tree/main/helm) `values.yml` by
 setting the environment variable `CODER_PROMETHEUS_ADDRESS` to `0.0.0.0:2112`.
 The environment variable `CODER_PROMETHEUS_ENABLE` will be enabled
-automatically.
+automatically. A Service Endpoint will also be exposed allowing Prometheus
+Service Monitors to be used.
 
 ### Prometheus configuration
 
@@ -53,6 +54,26 @@ scrape_configs:
           apps: "coder"
 ```
 
+To use the Kubernetes Prometheus operator to scrape metrics, you will need to
+create a `ServiceMonitor` in your Coder deployment namespace. Below is an
+example `ServiceMonitor`:
+
+```yaml
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: coder-service-monitor
+  namespace: coder
+spec:
+  endpoints:
+    - port: prometheus-http
+      interval: 10s
+      scrapeTimeout: 10s
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: coder
+```
+
 ## Available metrics
 
 <!-- Code generated by 'make docs/admin/prometheus.md'. DO NOT EDIT -->