docs: Document ENABLE_PROMETHEUS environment variable for v1.17.11

self-hosting/prometheus-metrics.mdx

@@ -488,6 +488,46 @@ Measures the performance of converting incoming gRPC requests to HTTP format bef
 
 ## Configuration
 
+### Enabling/Disabling Metrics Collection
+
+**Environment Variable**: `ENABLE_PROMETHEUS`
+
+**Default**: `true` (enabled)  
+**Values**: `true` | `false`
+
+The Portkey Enterprise Gateway allows you to completely disable Prometheus metrics collection if not needed for your deployment. When disabled, both the metrics middleware and the `/metrics` endpoint are deactivated, reducing overhead in environments where Prometheus monitoring is not required.
+
+**Configuration**:
+```bash
+# Disable Prometheus metrics (case-insensitive)
+ENABLE_PROMETHEUS=false
+
+# Enable Prometheus metrics (default behavior - can be omitted)
+ENABLE_PROMETHEUS=true
+```
+
+**Behavior**:
+- When `ENABLE_PROMETHEUS=false`:
+  - Metrics middleware is not registered
+  - The `/metrics` endpoint returns 404
+  - No metric collection overhead
+  - All custom and runtime metrics are disabled
+
+- When `ENABLE_PROMETHEUS=true` or unset (default):
+  - Full metrics collection enabled
+  - `/metrics` endpoint available
+  - All metrics described in this document are active
+
+**Use Cases**:
+- **Development environments** where metrics are not needed
+- **Resource-constrained deployments** to minimize overhead
+- **Security-sensitive environments** where metrics exposure is not desired
+- **Cost optimization** in serverless or pay-per-use infrastructure
+
+<Tip>
+For production deployments, keeping Prometheus metrics enabled is strongly recommended for observability, debugging, and performance monitoring.
+</Tip>
+
 ### Dynamic Metadata Label System
 
 The Portkey Enterprise Gateway supports dynamic metadata labeling through request-specific metadata injection. This powerful feature enables fine-grained observability across custom dimensions specific to your organization's structure and use cases.