[Python] Flatc stub compatibility with gRPC asyncio Interface

[Paul-Paquette]

Does the autogenerated stub code from flatc support using the aio interface in gRPC for the channel? Asyncio support was added to gRPC officially in 1.32, and I want to take advantage of that support.

I had tried simply changing the channel input to the stub initializer to a grpc.aio.insecure_channel() but had difficulty using the member functions of the stub with that channel, unlike the non-aio interface. So I figured I'd ask outright if this gRPC interface is supported before digging deeper.