Disable menu items during snapshot process

[rak-phillip]

Users can potentially quit Rancher Desktop while a snapshot operation(create/restore) is in progress.

This behavior is always present in macOS but can also happen on Windows and Linux, depending on environment customization.

Proposed Solution

Disable menu items on all platforms(macOS, Windows, Linux) while a snapshot operation is active.

macOS

• Settings...
• Quit Rancher Desktop

Windows & Linux

• Preferences
• Exit

[jandubois]

I don't think quitting or exiting should be completely disabled; they should (try to) cancel the current snapshot operation (once that functionality is implemented) and then still shut down the VM gracefully.

[rak-phillip]

Sounds good, maybe this issue will become solely focused on disabling preferences and then we can focus on the quitting/exiting behavior in #5999

[mook-as]

FWIW, I can reproduce on Windows via:

1. Start a snapshot (restore, in my case)
2. Using the tray menu, select Open main window
3. Use the keyboard shortcuts (Alt+F, etc.)

The keyboard shortcuts are unavailable until step 2 was completed.