configure auto expand for dataframe indexes (#42924)

creates the dataframe destination index with auto expand for replicas (0-1)

Author: Hendrik Muhs

x-pack/plugin/data-frame/src/main/java/org/elasticsearch/xpack/dataframe/persistence/DataframeIndex.java

@@ -13,6 +13,7 @@
 import org.elasticsearch.action.admin.indices.create.CreateIndexAction;
 import org.elasticsearch.action.admin.indices.create.CreateIndexRequest;
 import org.elasticsearch.client.Client;
+import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.xpack.core.dataframe.DataFrameField;
@@ -46,7 +47,8 @@ public static void createDestinationIndex(Client client, DataFrameTransformConfi
 
         // TODO: revisit number of shards, number of replicas
         request.settings(Settings.builder() // <1>
-                .put("index.number_of_shards", 1).put("index.number_of_replicas", 0));
+                .put(IndexMetaData.SETTING_NUMBER_OF_SHARDS, 1)
+                .put(IndexMetaData.SETTING_AUTO_EXPAND_REPLICAS, "0-1"));
 
         request.mapping(DOC_TYPE, createMappingXContent(mappings,
             transformConfig.getPivotConfig().getGroupConfig().getGroups(),