[BUG]: Remove 'New Window' Context Option for Apps Without Multi-Instance Support

[iamkartiknayak]

Currently, in Cosmic, some apps that don't support multiple instances such as Cosmic Settings and Cosmic App Store still display the "New Window" option in the app tray context menu. This can be confusing, as selecting "New Window" does nothing for these apps

[iamkartiknayak]

I should've opened this issue in the applets section, I suppose. If any dev is reading, please move it to the appropriate section. Thank you!