Document metrics grid aggregations in Discover

solutions/observability/infra-and-hosts/discover-metrics.md

@@ -112,6 +112,12 @@ Select specific values to focus on within the dimension. You can select up to 10
 
 {applies_to}`serverless: ga` {applies_to}`stack: ga 9.6+` When you [save the Discover session](/explore-analyze/discover/save-open-search.md#_save_a_discover_session), the selected dimensions and the metric search term are saved with that tab and restored when you reopen or duplicate the session.
 
+**Change how metrics are aggregated** {applies_to}`stack: ga 9.6+` {applies_to}`serverless: ga`
+:   You can change the default aggregation for each metric type:
+    - **Counter**: average, sum (default), minimum, and maximum
+    - **Gauge**: average (default), sum, minimum, and maximum
+    - **Histogram**: 50th percentile, 75th percentile, 90th percentile, 95th percentile (default), and 99th percentile
+
 **View metric charts in full screen**
 
 Select full screen ({icon}`full_screen`) to view the metric charts in full-screen mode.