Much as we did for podman, we should add a grpc listener to buildah. Because it wasn't built to be a service, for now, this will look more like `buildah unshare`, which will set up a listening socket, spawn a specified command with an environment variable pointing to that listening socket, and then wait for the command to finish. While the command is running, buildah will answer RPC requests on the listening socket. That should give us something we can test, and, later, any services which we hang off of that socket should be easy to add to podman's socket.