closes #3104 - add support for exposing prometheus metrics

CHANGELOG.md

@@ -58,6 +58,29 @@ https://nms.local/nodes/?name={{ obj.name }}
 Custom links appear as buttons at the top of the object view. Grouped links will render as a dropdown menu beneath a
 single button.
 
+### Prometheus Metrics ([#3104](https://github.com/digitalocean/netbox/issues/3104))
+
+NetBox now supports optionally exposing native Prometheus metrics from the application. [Prometheus](https://prometheus.io/)
+is a popular time series metric platform used for monitoring. NetBox exposes metrics at the `/metrics` HTTP endpoint, e.g.
+`https://netbox.local/metrics`. Metric exposition can be toggled with the `METRICS_ENABLED` configuration setting. Metrics
+are exposed by default.
+
+NetBox makes use of the [django-prometheus](https://github.com/korfuri/django-prometheus) library to export a number of
+different types of metrics, including:
+
+- Per model insert, update, and delete counters
+- Per view request counters
+- Per view request latency histograms
+- Request body size histograms
+- Response body size histograms
+- Response code counters
+- Database connection, execution, and error counters
+- Cache hit, miss, and invalidation counters
+- Django middleware latency histograms
+- Other Django related metadata metrics
+
+For the exhaustive list of exposed metrics, visit the `/metrics` endpoint on your NetBox instance.
+
 ## Changes
 
 ### New Dependency: Redis