[FIX] Use mangoapp when using mangohud with gamescope

[Etaash-mathamsetty]

This is how gamescope docs say to use mangohud with gamescope

Use the following Checklist if you have changed something on the Backend or Frontend:

• Tested the feature and it's working on a current and clean install.
• Tested the main App features and they are still working on a current and clean install. (Login, Install, Play, Uninstall, Move games, etc.)
• Created / Updated Tests (If necessary)
• Created / Updated documentation (If necessary)

[CommandMC]

Relevant docs for this change