Support ephemeral keys / tailscale logout

[uthark]

If golink is deployed as kubernetes, pod, then each time pod is rescheduled, golink register it self as go-%d and so on.

Per tailscale documentation, I could use ephemeral keys, then device is automatically removed within 48h. Also, per docs one could use tailscale logout to force removal of the service from tailscale.

It would be nice, if golink would capture SIGTERM and do proper logout in tailscale.

If you have any good workarounds, please share.