Bug#985074: x2goclient: [UX] SSH key login discoverability

[JCGoran <jcgoran@protonmail.com>]

Package: x2goclient
Version: 4.1.2.2-2
Severity: wishlist
X-Debbugs-Cc: jcgoran@protonmail.com

Dear Maintainer,

When a user either suspends or terminates a running session, they are
greeted by a prompt with the fields `Login` and `Password`, but there is no
mention of SSH keys. Of course, if the user just leaves the password blank
and tried to login, x2go will still connect because it's using the key
behind the scenes, but this is not indicated anywhere. I think it would be
much clearer if there was a checkbox on that particular screen, with a label
`Use SSH key`, and perhaps an optional path selector for the SSH key, which
would disable any input for the password field, giving the user a clear
indication that the SSH key would be used to login, and a password is not
required.

This is a _very_ minor issue, but can still potentially trip users up (in
fact, I must admit that I discovered the "leave the password blank when
using an SSH key" feature purely by accident).

Thanks,
Goran