Explain metrics endpoint availability on port 9100

Author: emyller

docs/docs/deployment-self-hosting/scaling-and-performance/monitoring.md

@@ -77,6 +77,8 @@ If you need additional AppDynamics setup options, you can find the other environ
 
 To enable the Prometheus `/metrics` endpoint, set the `PROMETHEUS_ENABLED` environment variable to `true`.
 
+When enabled, Flagsmith serves the `/metrics` endpoint on a standalone HTTP server on port 9100, separate from the main API server. This design ensures that metrics collection remains available even when the main API is under heavy load.
+
 The metrics provided by Flagsmith are described below.
 
 | Metric Name | Type | Description | Labels |