added type check for pipeline aggregator types in Transform initializ…

…ation (#1014) (#1029)

(cherry picked from commit cd99b0f)

Signed-off-by: n-dohrmann <noah@dohrmann.org>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Joanne Wang <109310487+jowg-amazon@users.noreply.github.com>

src/main/kotlin/org/opensearch/indexmanagement/transform/model/Transform.kt

@@ -77,6 +77,9 @@ data class Transform(
         aggregations.aggregatorFactories.forEach {
             require(supportedAggregations.contains(it.type)) { "Unsupported aggregation [${it.type}]" }
         }
+        aggregations.pipelineAggregatorFactories.forEach {
+            require(supportedAggregations.contains(it.type)) { "Unsupported aggregation [${it.type}]" }
+        }
         when (jobSchedule) {
             is CronSchedule -> {
                 // Job scheduler already correctly throws errors for this