Add a config to enable live wallpaper in desktop experience

Flag: android.app.enable_connected_displays_wallpaper
Test: atest FrameworksMockingServicesTests:WallpaperManagerServiceTests
Test: atest CtsWindowManagerDeviceMultiDisplay:android.server.wm.multidisplay.MultiDisplaySystemDecorationTests
Test: Run go/cd-smoke
Bug: 393354639
Change-Id: Iccd0f8a78a01a76ddfef0c0d763545f561681f78