Move the template, request handler, and HTTP/HTTPS server wiring out
of package main and into a new cmd/hello/helloserver package so the
server can be embedded in other binaries. The main package now only
constructs a helloserver.Server with the production addresses and
calls Run.
While here, drop the -http, -https, and -test-ip flags along with the
dev-mode template and fake-data fallbacks they enabled; the binary is
only run in production.
Updates tailscale/corp#32398
Change-Id: Id1d38b981733334cafc596021130f36e1c1eed67
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
