The hook is run before the environment is loaded or the config is
parsed.
This makes it a bit of a special case - it doesn't have the usual
KAMAL_XYZ environment variables, as we haven't parsed the config.
The use case for this is to do auth checking or setup. So for example
we can confirm you are logged in to a secret manager, and then you
can directly call it to load your secrets in the .kamal/.env file
using .dotenv's
[command substitution](https://github.com/bkeepers/dotenv?tab=readme-ov-file#command-substitution).
If curl is not available to download the docker install script, try
with wget instead.
If neither is available or both fail, return a simple failing script
so that we don't carry on regardless.
Fixes: https://github.com/basecamp/kamal/issues/395
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.
To avoid polluting the default SSH directory with lots of Kamal config,
we'll default to putting them in a `kamal` sub directory.
But also make the directory configurable with the `run_directory` key,
so for example you can set it as `/var/run/kamal/`
The directory is created during bootstrap or before any command that
will need to access a file.
