New timeseries function: Percentile Over Time (elastic#136761)

* New timeseries function: Percentile Over Time

* fixup capability

* comments

Author: pabloem

.swp

@@ -305,6 +305,30 @@ max_cost:double | cluster:keyword | time_bucket:datetime
 11.0            | qa              | 2024-05-10T00:07:00.000Z
 ;
 
+percentile_over_time
+required_capability: ts_command_v0
+required_capability: percentile_over_time
+// tag::percentile_over_time[]
+TS k8s
+| STATS p95_cost=MAX(PERCENTILE_OVER_TIME(network.cost, 95)), p99_cost=MAX(PERCENTILE_OVER_TIME(network.cost, 99)) BY cluster, time_bucket = TBUCKET(1minute)
+// end::percentile_over_time[]
+| SORT p95_cost DESC, time_bucket DESC, cluster | LIMIT 10;
+
+// tag::percentile_over_time-result[]
+p95_cost:double | p99_cost:double | cluster:keyword | time_bucket:datetime
+12.375          | 12.375          | prod            | 2024-05-10T00:17:00.000Z
+12.375          | 12.375          | qa              | 2024-05-10T00:01:00.000Z
+12.34375        | 12.36875        | qa              | 2024-05-10T00:06:00.000Z
+12.25           | 12.25           | prod            | 2024-05-10T00:19:00.000Z
+12.0125         | 12.1025         | qa              | 2024-05-10T00:07:00.000Z
+11.98125        | 12.39625        | staging         | 2024-05-10T00:09:00.000Z
+11.98125        | 12.09625        | prod            | 2024-05-10T00:00:00.000Z
+11.875          | 11.875          | prod            | 2024-05-10T00:15:00.000Z
+11.875          | 11.875          | qa              | 2024-05-10T00:09:00.000Z
+11.80625        | 11.96125        | prod            | 2024-05-10T00:08:00.000Z
+
+;
+
 avg_of_avg_over_time
 required_capability: ts_command_v0
 TS k8s | STATS avg_cost=avg(avg_over_time(network.cost)) BY cluster, time_bucket = bucket(@timestamp,1minute) | SORT avg_cost DESC, time_bucket DESC, cluster | LIMIT 10;