Support a Custom Deserialiser on JSON Kafka Load Routine

[rlapao]

Feature request

Is your feature request related to a problem? Please describe.
Yes. I was trying to consume a JSON Kafka topic that uses Confluent Schema Registry (JSON Schema) getting the following error: previous task aborted because of illegal json started with . This happens due to the format of Confluent JSON Schema Registry messages is schema_id { ... valid json message ... } which makes this message an invalida JSON message.

Describe the solution you'd like
Support a Custom Deserialiser on JSON Kafka Load Routine.

Describe alternatives you've considered
Support Confluent Schema Registry format in JSON Kafka Load Routines.

[jaogoy]

Routine Load supports loading avro formt data + schema registry.
I wonder that are your schema registry messages in the data flow the same as normal data messages?