Added csv tests and capability for sample and values on unsigned longs

Author: ivancea

x-pack/plugin/esql/qa/testFixtures/src/main/resources/stats_sample.csv-spec

@@ -64,6 +64,20 @@ sample_boolean:boolean | sample_datetime:datetime
 [false, true, true]    | [1985-11-21T00:00:00.000Z, 1986-06-26T00:00:00.000Z, 1986-08-28T00:00:00.000Z] | [1.83, 2.03, 2.08]   | [10001, 10002, 10003]  | [Bezalel, Georgi, Parto] | [2, 4, 5] 
 ;
 
+sample unsigned_long
+required_capability: agg_values_sample_unsigned_long
+
+FROM ul_logs
+| STATS v = MV_SLICE(MV_SORT(SAMPLE(bytes_in, 99)), 3, 5)
+| MV_EXPAND v
+;
+
+v:ul
+0
+74330435873664882
+154551962150890561
+;
+
 
 multivalued
 required_capability: agg_sample

x-pack/plugin/esql/qa/testFixtures/src/main/resources/unsigned_long.csv-spec

@@ -194,3 +194,14 @@ s:double | bytes_in:ul | bytes_out:ul
 1.0      | 1957665857956635540          | 352442273299370793
 1.0      | 2408213296071189837          | 419872666232023984
 ;
+
+values
+required_capability: agg_values_sample_unsigned_long
+from ul_logs | stats v = values(bytes_in) | MV_EXPAND v | SORT v | LIMIT 3;
+
+v:ul
+0
+74330435873664882
+154551962150890561
+;
+

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -97,6 +97,11 @@ public enum Cap {
          */
         AGG_MAX_MIN_UNSIGNED_LONG,
 
+        /**
+         * Accept unsigned longs on VALUES and SAMPLE aggregations.
+         */
+        AGG_VALUES_SAMPLE_UNSIGNED_LONG,
+
         /**
          * Does ESQL support async queries.
          */