Document plugin-provided metrics at the standard /metrics endpoint

source/administration-guide/scale/deploy-prometheus-grafana-for-performance-monitoring.rst

@@ -122,6 +122,8 @@ What's collected?
 
 Mattermost provides :ref:`custom metrics <administration-guide/scale/performance-monitoring-metrics:custom Mattermost metrics>` and :ref:`standard Go metrics <administration-guide/scale/performance-monitoring-metrics:standard go metrics>` that can be used to monitor your system's performance.
 
+When the ``AggregatePluginMetrics`` feature flag is enabled, plugin-provided metrics are included in the same ``/metrics`` scrape target and can be filtered by the ``plugin_id`` label.
+
 Next steps
 ----------
 

source/administration-guide/scale/performance-monitoring-metrics.rst

@@ -176,6 +176,11 @@ Plugin metrics
 - ``mattermost_plugin_multi_hook_server_time``: Time for the server to execute multiple plugin hook handlers in seconds.
 - ``mattermost_plugin_multi_hook_time``: Time to execute multiple plugin hook handler in seconds.
 
+The metrics above are measured by the Mattermost server as it executes plugin code. From Mattermost v11.8.0, plugin-provided Prometheus metrics can also be exposed through the standard Mattermost ``/metrics`` endpoint when the ``AggregatePluginMetrics`` feature flag is enabled. Aggregated plugin metrics include a ``plugin_id`` label, based on the plugin's manifest ID, so admins can identify which plugin produced each metric.
+
+.. note::
+  ``AggregatePluginMetrics`` is disabled by default and must be enabled before plugin-provided metrics are included in the ``/metrics`` response.
+
 Shared metrics
 ~~~~~~~~~~~~~~