Add support for multiple Klipper instances

[Nojwe]

• Automatically discover all Klipper instances in $HOME following the pattern printer_data or printer_[instance name]_data
• Prompt user to select discovered instances for backup to github. Selected instances will be added to the .env file.
• Default to backing up the entire config directory; notes users can modify that by editing .env
• Allow user to select which Moonraker instance(s) to install the update manager on. Uses same instance list as the backup process
• Only restart specific Moonraker instance when the update manager is added

[Tylerjet]

@Staubgeborener I think you saw more about this in the issue that was open, I'll leave it up to you.
I believe you can already add the path in the current implementation so if this is just automating that process on install to find those paths and place them in the env, it seems good to me.

[Staubgeborener]

Unfortunately, I don't have the time to test everything at the moment, as I would need to set up an extra multi-instance for this. I'll keep it in mind and hopefully test it soon. If everything works, I'll merge it.