EC data write as data streams

Today, EC write is done in a discrete fashion via GRPC where each chunk is modeled as a WriteChunk request. Because of that, we have to implement a big chunk size to archive stream-like performance, and other unnatural improvements like ZeroCopy on GRPC. 

GRPC and discrete data transfer protocol is not the perfect fit for data transfer. We should move to use native stream, leverage Netty, to implement EC writes.