Append index name for the source of the cluster put-mapping task (#52690)

Add index name(s) into the source for the cluster state update done when putting mapping.
This ensures that the pending tasks API includes information on source indices.

server/src/main/java/org/elasticsearch/cluster/metadata/MetaDataMappingService.java

@@ -33,6 +33,7 @@ import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.Priority;
+import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.unit.TimeValue;
@@ -326,7 +327,7 @@ public class MetaDataMappingService {
     }
 
     public void putMapping(final PutMappingClusterStateUpdateRequest request, final ActionListener<ClusterStateUpdateResponse> listener) {
-        clusterService.submitStateUpdateTask("put-mapping",
+        clusterService.submitStateUpdateTask("put-mapping " + Strings.arrayToCommaDelimitedString(request.indices()),
                 request,
                 ClusterStateTaskConfig.build(Priority.HIGH, request.masterNodeTimeout()),
                 putMappingExecutor,