Instead of using `kamal envify` to generate the .env file, we now assume
that it will be in place for us.
Options in place of `kamal envify`:
1. Pre-generate the .env file
2. Create the env file in the `.pre-init` hook
3. Log into a secret store/check you are logged in in the pre-init hook
Then use .dotenv command and variable substitution to interpolate the
secrets.
To avoid conflicts with other tools that use .env files, read the files
from .kamal/ instead.
If there are no matching env files in .kamal/, we'll read from the
project root for now and emit a warning.
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.
