[Java SDK] Implement automatic consumer group rebalancing

[chiradip]

Title: [Java SDK] Implement automatic consumer group rebalancing

Description:
Current SDK requires manual consumer group management without automatic rebalancing.

Proposed Solution:

// Automatic rebalancing
ConsumerGroup group = client.joinConsumerGroup(
    "my-group",
    ConsumerGroupConfig.builder()
        .rebalanceStrategy(RebalanceStrategy.RANGE)
        .sessionTimeout(Duration.ofSeconds(30))
        .heartbeatInterval(Duration.ofSeconds(3))
        .onPartitionsAssigned(partitions -> {...})
        .onPartitionsRevoked(partitions -> {...})
        .build()
);

[numinnex]

The consumer group rebalancing is on the server side, there were attempts for client side rebalancing from kafka, but they are going back to server side incremental rebalance.

[numinnex]

I think we should close this for now. We have an RFC similar to the KIP that I've mentioned in comment above, but for now we have other priorities.