SSH has the capability to route traffic through a proxy. This is done using the -J xxx argument. The ProxyJump can be used for security purposes by limiting access to remote servers to specific IP addresses.

Previously it had to use wp-cli with a proxy in between. The only somewhat practical way was adding it to your personal ~/.ssh/config:

Host production
  HostName xxx.xxx.xxx.xxx
  ProxyCommand ssh -q -W %h:22 vagrant

But this is technical and has to be done on every single machine in a team of multiple contributors.

This PR adds an option proxyjump to the alias specification so the wp-cli.yml config file can specify a comon proxy for all traffic to go through.

The change also includes a fix for the key attribute. It was part of the options for vagrant but did not seem possible for regular SSH commands, even though is can be usefull.