Support binding to unix domain sockets

[phue]

It would be nice if shiny run would expose a cli option to bind to unix domain sockets instead of tcp ports.
uvicorn already supports this via the --uds flag.

This already works in python (as run_app() passes **kwargs on to uvicorn.run()):

from shiny import run_app

run_app("app:app", uds="/tmp/shiny.sock")

But in the shiny run cli, additional arguments are not allowed.