Raise a more specific error for incompatible schema from the registry

[HarlemSquirrel]

Right now, the schema from a Confluent Schema Registry is assumed to be AVRO which is the default. If it is not, we still attempt to parse it and then can get somewhat confusing errors like MultiJson::ParseError for PROTOBUF schema.

It would be nice to throw a more specific error here like

class AvroTurf
  class Messaging
    class IncompatibleSchemaError < StandardError; end
   
    def fetch_schema(subject:, version: 'latest')
      schema_data = registry.subject_version(subject, version)
      schema_id = schema_data.fetch('id')
      schema_type = schema_data["schemaType"]
      if schema_type.present? && schema_type != "AVRO"
        raise IncompatibleSchemaError("The #{schema_type} schema for #{subject} is incompatible.")
      end
      schema = Avro::Schema.parse(schema_data.fetch('schema'))
      [schema, schema_id]
    end
  end
end

For the long-run, it would be awesome to get maybe a new gem that could handle all three schema types that the registry supports: AVRO, PROTOBUF, and JSON. I know it has been brought up before in #158 to reuse some of this gem.

[dasch]

Could you whip up a PR for this?

[HarlemSquirrel]

@dasch just opened #219