Introduction of Qt gRPC

There are multiple users and multiple use cases who prefer or need to use gRPC and Protocol Buffers to implement service-oriented architectures (https://en.wikipedia.org/wiki/Service-oriented_architecture) and use Qt for this.

gRPC and Protocol Buffers on their own are different in their purpose. While gRPC (https://en.wikipedia.org/wiki/GRPC) provides an RPC implementation, Protocol Buffers (https://en.wikipedia.org/wiki/Protocol_Buffers) define a format for data serialisation and provide a description language along with a code generator. Even though both parts are orthogonal, after many years in the field, gRPC and Protocol Buffers are together in a wast majority of cases. Users define their data and messages in "proto" files, use one of the code generators and then use this code in their implementations to either be able to talk to a remote service on the client side or provide a service for other clients.

We intent or provide a solution in Qt makes it easy to use both technologies in Qt-based applications, let it be on the client or on the server side. For example, Protocol Buffers should well map to standard Qt types and gRPC should seamlessly integrate in Qt using its standard mechanisms for messages and responses. Moreover with this implementation users should be able to develop for example a Qt client which is able to "talk via gRPC" to a service implemented in Java, or Go.

This epic collects tasks required for the first version of these implementation. 

Some other references:

• https://grpc.io/docs/what-is-grpc/introduction/
• https://grpc.io/docs/what-is-grpc/core-concepts/

A large collection of information, projects, videos, examples and even public services: https://github.com/grpc-ecosystem/awesome-grpc