Exposes a local port on the tailnet under a chosen hostname. Raw TCP by
default; --http or --https reverse-proxy with Tailscale-User-* identity
headers from WhoIs, matching tailscaled's serve header conventions.
Useful as a one-shot to put a dev server on the tailnet.
Fixes#19467
Change-Id: I79f63cfbbedf7e40cf0f1f51cbae8df86ae90cdf
Signed-off-by: Fernando Serboncini <fserb@tailscale.com>