default CompletableFuture<BalanceResponse> balanceRSGroup(String groupName) {
    return balanceRSGroup(groupName, BalanceRequest.defaultInstance());
  }
Balance regions in the given RegionServer group
@param groupName the group name
@return BalanceResponse details about the balancer run
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncAdmin.java