Hooks: pre-proxy-reboot

Run before rebooting the kamal-proxy container when you call kamal proxy reboot.

If you have the hook disabling the current server in an external load balancer and use the --rolling flag, you can use this for a zero-downtime proxy reboot.

With a rolling reboot, the hook will be called once for each server, with KAMAL_HOSTS containing the current server. With a non-rolling reboot, it will be called just once.

Use the post-proxy-reboot hook to re-enable the server.