[Docs] Generate full list of metrics in user docs (#30388)

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/usage/metrics.md

@@ -33,11 +33,19 @@ Then query the endpoint to get the latest metrics from the server:
 
 The following metrics are exposed:
 
-??? code
+## General Metrics
 
-    ```python
-    --8<-- "vllm/engine/metrics.py:metrics-definitions"
-    ```
+--8<-- "docs/generated/metrics/general.md"
+
+## Speculative Decoding Metrics
+
+--8<-- "docs/generated/metrics/spec_decode.md"
+
+## NIXL KV Connector Metrics
+
+--8<-- "docs/generated/metrics/nixl_connector.md"
+
+## Deprecation Policy
 
 Note: when metrics are deprecated in version `X.Y`, they are hidden in version `X.Y+1`
 but can be re-enabled using the `--show-hidden-metrics-for-version=X.Y` escape hatch,