Schema Registry support through PulsarKafkaProducer

[briandoran]

Is your feature request related to a problem? Please describe.
In order to minimise integration issues with Kafka/Pulsar I am wondering if its possible to use the Apache Kafka producer API to specify using AVRO schemas in Pulsar? It looks like this can just be done through the pulsar ProducerBuilder API pulsarClient.newProducer(avro).create(); which returns a pulsar.Producer rather than a apache.kafka.Producer. I wanted to keep changes to integration to a minimum which is fine when not specifying a schema. new PulsarKafkaProducer<>(props) vs new KafkaProducer<>(props)

Describe the solution you'd like
As discussed with @sijie on Slack a perfect solution would be adding a new Schema parameter to the PulsarKafkaProducer?

new PulsarKafkaProducer<>(props, schema)

This would allow the schema will be passed down to the internal pulsar client.

We also spoke about a integration with external schema registry, and implementing a ConfluentSchema which talks to confluent schema registry. so it will use confluent schema registry and confluent converters to do serialization and deserialization.

so the code would be something like:

`Schema schema = ConfluentSchema.builder()
.withSchemaRegistryUrl(...)
.withKeySerializer(...)
.withValueSerializer(...);

Producer<> producer = new PulsarKafkaProducer(props, schema);`

Great work on the support BTW, the slack portal is invaluable for getting great information with quick responses.