Using `tmux`, we can spawn a bunch of `picocom` processes for the serial
ports connected to other server's console ports. The
_serial-terminal-server_ service manages the `tmux` server process,
while the individual _serial-terminal-server-window@.service_ units
create a window in the `tmux` session.
The serial terminal server runs as a dedicated user. The SSH server is
configured to force this user to connect to the `tmux` session. This
should help ensure the serial consoles are accessible, even if the
Active Directory server is unavailable.
Dustin