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.
