Docker container for generating protobuf code. Right now used in CI only for other projects. Smallish image size (~220mb); unfortunately the grpc-swift plugins cause it to blow out as they're statically linked (so don't need foundation or the swift dependencies). Not copying them across will save ~100mb in space.

TODOS

Build the grpc-web plugins in the dockerfile, rather than downloading built versions
Use CMake/Bazel for building the c grpc plugins - CMake dockerfile