Calling `load_envs` again does not load updated env variables, because
Dotenv does not overwrite existing values.
To fix this we'll store the original ENV and reset to it before
reloading.
https://github.com/basecamp/kamal/issues/512
The env check is not needded anymore as all the commands rely on the
env files having already been created remotely.
The only place the env is needed is when running `kamal env push` and
that will still raise an apropriate error.
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.
