Using Scripted Avg Class in AvgAggregationBuilder in place of double

Signed-off-by: Kshitij Tandon <tandonks@amazon.com>

Author: tandonks

src/main/kotlin/org/opensearch/indexmanagement/rollup/util/RollupUtils.kt

@@ -240,13 +240,13 @@ fun Rollup.rewriteAggregationBuilder(aggregationBuilder: AggregationBuilder): Ag
                 .combineScript(
                     Script(
                         ScriptType.INLINE, Script.DEFAULT_SCRIPT_LANG,
-                        "def d = new double[2]; d[0] = state.sums; d[1] = state.counts; return d", emptyMap(),
+                        "def d = new org.opensearch.search.aggregations.metrics.ScriptedAvg(state.sums, state.counts); return d", emptyMap(),
                     ),
                 )
                 .reduceScript(
                     Script(
                         ScriptType.INLINE, Script.DEFAULT_SCRIPT_LANG,
-                        "double sum = 0; double count = 0; for (a in states) { sum += a[0]; count += a[1]; } return sum/count", emptyMap(),
+                        "double sum = 0; double count = 0; for (a in states) { sum += a.getSum(); count += a.getCount(); } return sum/count", emptyMap(),
                     ),
                 )
         }

src/test/kotlin/org/opensearch/indexmanagement/rollup/interceptor/RollupInterceptorIT.kt

@@ -1103,7 +1103,8 @@ class RollupInterceptorIT : RollupRestTestCase() {
                 },
                 "aggs": {
                     "sum_passenger_count": { "sum": { "field": "passenger_count" } },
-                    "max_passenger_count": { "max": { "field": "passenger_count" } }
+                    "max_passenger_count": { "max": { "field": "passenger_count" } },
+                    "value_count_passenger_count": { "value_count": { "field": "passenger_count" } }
                 }
             }
             """.trimIndent()