feat[balance_strategy]: announcing a new round robin balance strategy

[kzinglzy]

There is a different behavior between

• sarama's roundrobin balance strategy

   // pseudo code
   for topic, partitions := range allTopicPartitions {
   	i := 0
   	for partition := range allPartitions {
   		consumer := allconsumers[i % len(allconsumers)]
   		consumer.assign(topic, partition)
   		i += 1
   	}
   }

• kafka java client's roundrobin balance strategy:

   // pseudo code
   i := 0
   for partition := range AllSortedPartitions {
   	consumer := allconsumers[i % len(allconsumers)]
   	consumer.assign(topic, partition)
   	i += 1
   }

In some case, sarama's implementation may incur skewed partitions,
for example:

// balance_strategy_test.go/TestBalanceStrategyRoundRobin:tests
{
    members: map[string][]string{"M": {"T1", "T2", "TT2"}, "M2": {"T1", "T2", "TT2"}, "M3": {"T1", "T2", "TT2"}},
    topics:  map[string][]int32{"T1": {0}, "T2": {0}, "TT2": {0}},
    expected: BalanceStrategyPlan{
        // there are three members and topics, however all the topics and partitions are assign to a single member
	"M": map[string][]int32{"T1": {0}, "T2": {0}, "TT2": {0}},
},

This PR provides the "really" roundrobin implementation that same as kafka java client did

[dnwe]

@kzinglzy I'm happy to approve the changes, although I do wonder if the original implementation of the round robin strategy should just be considered flawed and we should replace it with your correct implementation rather than adding this as a new alternative strategy? Whilst I know it would technically be a potentially unexpected change of behaviour for people, it still seems like the right thing to do.

@bai thoughts? I wonder if we should rename the old strategy to something with "legacy" in the name and then make @kzinglzy's implementation the "RoundRobinBalancer" and just mention the change of behaviour in the next release notes?

[kzinglzy]

@kzinglzy I'm happy to approve the changes, although I do wonder if the original implementation of the round robin strategy should just be considered flawed and we should replace it with your correct implementation rather than adding this as a new alternative strategy? Whilst I know it would technically be a potentially unexpected change of behaviour for people, it still seems like the right thing to do.

@bai thoughts? I wonder if we should rename the old strategy to something with "legacy" in the name and then make @kzinglzy's implementation the "RoundRobinBalancer" and just mention the change of behaviour in the next release notes?

as mentioned previously, the old implementation of round robin strategy is not so "standard" , in some cases even wrong (e.g. skewed partitions), thus, it may be ok to replace it with a more "standard" implementation directly

so this PR should be considered as a bug fixing :P

[dnwe]

Yeah that was my thinking. To my reading our original implementation was just incorrect, I can't think of a good reason why anyone would prefer it and I think we should accept your PR as a replacement that corrects the behaviour to match the original intention.

[bai]

I think it'd be OK to push this new strategy as a replacement (essentially a fix) and rename current one to Legacy.

[kzinglzy]

@bai the original implementation has been replaced

Um... CI failed, looks like a test env issue?

[bai]

Looks like a change in GitHub Actions broke CI. I've pushed a fix in #1862. Could you please rebase off of master?

[kzinglzy]

@bai please take a look, ready for merge