Protobuf Support

[devlap2]

Expected Behavior
I'd like there to be a Transformer of ProtobufToObjectTransformer. The Transformers class should include a fromProto function and a toProto function.

Current Behavior
There is no Protocol Buffers support in Spring Integration at all.

Context
Protocol Buffers are a popular and wide used mechanism for serializing structured data. This is a standard in the big data development and support to it will, later on, enable the development of grpc support.

[artembilan]

I suggest to align the impl with existing Avro transformers - SimpleFromAvroTransformer & SimpleToAvroTransformer: FromProtobufTransformer and ToProtobufTransformer.

We also might borrow some ideas from Spring Cloud Function to support gRPC channel adapters: https://spring.io/blog/2021/12/02/spring-cloud-function-3-2-is-out.

See also: #2626

and contribution is welcome: https://github.com/spring-projects/spring-integration/blob/main/CONTRIBUTING.adoc !

[markusherbert]

Agree with @artembilan. This can be renamed to Protobuf & grpc support / we should add another grpc focused ticket. Grpc support is super important either.