Consider using defaultApiTimeoutMs in AsyncKafkaConsumer#unsubscribe

This is followup from https://github.com/apache/kafka/pull/16673#discussion_r1717009724

AsyncKafkaConsumer#unsubscribe uses Long.MAX_VALUE to calculate deadline. However, most of AsyncKafkaConsumer operations use default.api.timeout.ms if users don't specify a timeout. In design document, it also mentions that using default.api.timeout.ms as default timeout.