Java.util.ConcurrentModificationException error when rebalance

[gosonzhang]

When there are many consumer groups in the cluster and frequent load balancing, the Master will report the following error:

which is caused by the modification of the subGroups object in the balanceCluster:

https://github.com/apache/incubator-inlong/blob/master/inlong-tubemq/tubemq-server/src/main/java/org/apache/inlong/tubemq/server/master/balance/DefaultLoadBalancer.java#L209

we need to fix the bug

[gosonzhang]

Optimization items:

1. Modify the usage mode of the subGroups object to be read-only processing;
2. Adjust the log printing to output the set of consumer groups affected by each abnormality;
3. Modify the consumption information acquisition of the consumer group, and add the check that the result is null;
4. When optimizing the processing of consumer events, the list is changed from judging the size to judging whether it is empty