Use pkg-config to configure grpc plugin

Use pkg-config to configure grpc plugin

- Check for libgrpc++ instead of libgrpc
- Add check for libprotobuf
- Add configure options --with-libgrpc++, --with-libprotobuf and --with-libprotobuf-c
- Add precious variable PROTOC for path to the protoc compiler
- Add precious variable PROTOC_C for path to the protoc-c compiler
- Add precious variable GRPC_CPP_PLUGIN for path to the grpc_cpp_plugin binary

Fixes #1817