Add ES|QL SAMPLE to list the agg functions in docs (elastic#133808)

* Add ES|QL SAMPLE to list the agg functions in docs

* add to list

Author: jan-elastic

docs/reference/query-languages/esql/_snippets/lists/aggregation-functions.md

@@ -6,6 +6,7 @@
 * [`MEDIAN_ABSOLUTE_DEVIATION`](../../functions-operators/aggregation-functions.md#esql-median_absolute_deviation)
 * [`MIN`](../../functions-operators/aggregation-functions.md#esql-min)
 * [`PERCENTILE`](../../functions-operators/aggregation-functions.md#esql-percentile)
+* [`SAMPLE`](../../functions-operators/aggregation-functions.md#esql-sample)
 * [preview] [`ST_CENTROID_AGG`](../../functions-operators/aggregation-functions.md#esql-st_centroid_agg)
 * [preview] [`ST_EXTENT_AGG`](../../functions-operators/aggregation-functions.md#esql-st_extent_agg)
 * [`STD_DEV`](../../functions-operators/aggregation-functions.md#esql-std_dev)

docs/reference/query-languages/esql/functions-operators/aggregation-functions.md

@@ -36,6 +36,9 @@ The [`STATS`](/reference/query-languages/esql/commands/stats-by.md) command supp
 :::{include} ../_snippets/functions/layout/percentile.md
 :::
 
+:::{include} ../_snippets/functions/layout/sample.md
+:::
+
 :::{include} ../_snippets/functions/layout/st_centroid_agg.md
 :::