Add a new control/tsp package providing a client for speaking the
Tailscale protocol to a coordination server over Noise, along with a
cmd/tsp binary exposing it as a low-level composable tool for
generating keys, registering nodes, and issuing map requests.
Previously developed out-of-tree at github.com/bradfitz/tsp; imported
here without git history.
Updates #12542
Change-Id: I6ad21143c4aefe8939d4a46ae65b2184173bf69f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
