Add ssh type keys and a `ghost ssh` command to allow to manage ssh connections

[nir0s]

It would be nice to have an ssh type key which will allow me to run something like ghost ssh my-server to automatically connect to a server based on config found in that key.

This means we would add a new "type" system to keys where an ssh type key contains preset values (ssh key path or string, connection string, etc..).

I could then do:

ghost put my-server conn='ubuntu@10.10.10.1' ssh_key=$(cat ~/.ssh/my-key) --key-type ssh

or

ghost put my-server conn='ubuntu@10.10.10.1' ssh_key_path=cat ~/.ssh/my-key --key-type ssh

and then:

ghost ssh my-server which will connect to it.

If the key is not of type ssh, it'll notify me that it's not an ssh type key.