Feat: make app background execution configurable

[M61ss]

Platform: Windows 11
Installation: windows-latest-x64.exe (build-e7e54042)

I found no opened and closed issue that match mine.

Actual behaviour

Now the application doesn't allow to the user to define the desktop app behaviour when it gets closed. For now, it is possible only using the Windows system tray.

Desired behaviour

I think that could be nice to let users to decide whether the app should keep running in background or completely stop.

Step to reproduce

1. Open the desktop app
2. Wait for Open WebUI launch on the browser
3. Close the desktop app using Windows' 'x'
4. Connect from the broswer to Open WebUI: it is still running

If you are on Windows you can check this also looking at the system tray.

[tjbck]

Addressed in the latest.