Add an outsource=true option when launching via ssh to go back to the terminal spawning approach

[chipsenkbeil]

Due to problems with ssh2-rs and not being able to upgrade wezterm-ssh (see #48) right now, we need another way to execute DistantLaunch. Should do the old process of termopen(...) with an ssh command, reading the result to look for the DISTANT CONNECT -- <PORT> <KEY> and then running DistantConnect programmatically.

Will require DistantConnect to support supplying the key programmatically. Probably shouldn't expose this in the command but instead allow it as part of editor.connect(...).

[chipsenkbeil]

We were able to upgrade to support libssh alongside ssh2-rs.

This is not an issue to be handled by the plugin, but instead upstream distant. I don't plan to re-add the ssh terminal option within the plugin.

What would be nice is the upstream chipsenkbeil/distant#193, which I'm hopeful would provide more stability in the pure SSH implementation of distant.