Kafka client Java API wrapper

[merlimat]

Recreated PR from #753

Motivation

Add a Kafka API wrapper based on Pulsar client library.

This will allow existing application using the Kafka client library to publish or suscbribe to a Pulsar topic without any code change.

This first iteration is targeting the Kafka high-level consumer with managed offsets, with or without auto-commit.

Examples and documentation on the website will follow this PR.

Modifications

• Add implementation of Kafka Producer and Consumer interfaces that internally use Pulsar client library
• Use Maven shading plugin to replace KafkaProducer class with PulsarKafkaProducer in the jar

Result

The org.apache.pulsar:pulsar-client-kafka-compact artifact will be a drop-in replacement for org.apache.kafka:kafka-clients.