By default look for the env file in .kamal/env to avoid clashes with
other tools using .env.
For now we'll still load .env and issue a deprecation warning, but in
future we'll stop reading those.
This allows the user to make any necessary configuration changes to
Docker before setting up any containers, allowing those configuration
changes to take effect from the outset.
Provide pre and post reboot hooks for Traefik, that can be used to
remove/add to an external load balancer to prevent requests from being
sent during the reboot.
Works best with the --rolling setting, where each hook is called once
per host.
