Producer and consumer optimizations

[fbeltrao]

Following changes have been made

• Default value type is byte[] from string, converter byte[] -> string has been updated. Goal is to offer best performance by default and let consumer deserialize at function level (Avro and Protobuf deserialization still supported)
• Trigger and output attribute have same constructor signature (brokerList, topic)
• Using a single librdkafka producer per configuration. Serialization for IAsyncCollector is added using DependentProducerBuilder
• Using producer async in output binding. The previous usage of Flush was blocking the thread
• Cleaned up the KafkaListener, passing deserialisers as parameters (removed KafkaListenerAvro and Protobuf)
• Added asynchronous commit strategy, saving offsets in background every 200ms (after a few tests the closest accuracy comparing to previous implementation).
• Added tests for KafkaProducerFactory and KafkaListenerFactory

Fixes: #72, #71, #70