Support additional terminals

[13hannes11]

Can you please add support for a few different terminals if that's possible? I think GNOME console is shipped by default nowadays instead of GNOME terminal. Some on the KDE side would be nice to.

Originally posted by @bbhtt in flathub/flathub#5400 (comment)

Suggested terminals to support for now

• Gnome Console
• Konsole
• Xfce Terminal

For some inspiration see:
https://github.com/Dvlv/BoxBuddyRS/blob/master/src/utils.rs#L230

• Check terminals at application startup and select one
• Be able to configure which terminal to use
  • Handle case where selected terminal is not present anylonger