Add vcpkg recipes to GRPC, ProtoBuf examples

GRPC, protobuf examples rely on upstream tools and libraries to work. Installing these, and telling CMake about it on all platforms is not straightforward.

Anyhow, the dependencies are supported by vcpkg, so we can add vcpkg.json files to each example.

Goal is that users can open & run the example on any machine, and Qt Creator fetches the external protobuf/grpc dependencies automatically.