[v2.x] Partition assignment

[mateusjunges]

Kafka Clients allows you to implement your own partition assignment strategies for consumers.

This PR allows to specify which partitions a consumer should consume from.

In the following example, this consumer will only consume messages from the my-awesome-topic partitions 2, and 3. Messages from any other partition won't be handled by this consumer.

Kafka::createConsumer()
    ->assignPartitions([
        new TopicPartition('my-awesome-topic', 2),
        new TopicPartition('my-awesome-topic', 3),
    ])
    ->withHandler(function (ConsumedMessage $message) {
        // Handle the message here
    })->build();

$consumer->consume();