source converter support configure

[elgca]

The configuration of the source converter is not supported. I can't set schema.enable = false when I use JsonConverter. It also cannot set the schema.registry.url for KafkaAvroDeserializer.

{
    ...
    "source.key.converter" : "org.apache.kafka.connect.json.JsonConverter",
    "source.key.converter.schemas.enable" : "false",
    "source.value.converter" : "org.apache.kafka.connect.json.JsonConverter",
    "source.value.converter.schemas.enable" : "false",
    ...
}

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @elgca to sign the Salesforce.com Contributor License Agreement.