Deprecate ssh and ssh_auto transport plugin

[agoscinski]

I would say we do this for the v2.8.0 release when ssh_async is feature complete. Maybe @khsrali could you write here (or link to a resource) what is needed so ssh_async can replace the other ssh transport plugins.

[khsrali]

Just talked to @agoscinski

We'll have to investigate if all authentication infos, supported by paramiko is also supported by asyncssh

One thing that we agreed it has to change before the release is to change machine_or_host in core.ssh_async to host_keyword so it would allow for a smoother transition.