Update UDS example with socket paths determined at runtime

[kriswuollett]

Feature Request

Motivation

Workaround and Rust education for closure capture requirement that currently only a static path is used:

tonic/examples/src/uds/client.rs

Lines 16 to 28 in c30cb78

	// We will ignore this uri because uds do not use it
	// if your connector does use the uri it will be provided
	// as the request to the `MakeConnection`.
	let channel = Endpoint::try_from("http://[::]:50051")?
	.connect_with_connector(service_fn(|_: Uri| {
	let path = "/tmp/tonic/helloworld";
	// Connect to a Uds socket
	UnixStream::connect(path)
	}))
	.await?;
	let mut client = GreeterClient::new(channel);

Proposal

Use the ustr crate to remove reliance on only a static hard-coded path.