Support protobuf deserialization from Schema Registry and without a generated descriptor

[sauljabin]

It's necessary that confluent-kafka-python provides support for this. It has it for java.
Right now the DESCRIPTOR is needed https://github.com/confluentinc/confluent-kafka-python/blob/master/src/confluent_kafka/schema_registry/protobuf.py#L482.

1. Extract the MessageIndexes https://github.com/confluentinc/schema-registry/blob/master/protobuf-serializer/src/main/java/io/confluent/kafka/serializers/protobuf/AbstractKafkaProtobufDeserializer.java#L139
2. Get the message name from the schema https://github.com/confluentinc/schema-registry/blob/master/protobuf-serializer/src/main/java/io/confluent/kafka/serializers/protobuf/AbstractKafkaProtobufDeserializer.java#L140
3. Make the FileDescriptorSet from the proto file got from schema registry (this is the blocker right now)
4. Get the class using the message name
5. Instantiate the class

Another alternative if using buf:
https://buf.build/docs/bsr/reflection/overview
https://googleapis.dev/python/protobuf/latest/google/protobuf/message_factory.html

[sauljabin]

confluentinc/confluent-kafka-python#1174

[sauljabin]

confluentinc/confluent-kafka-python#1852