Add more info in the overlay

[utkarshdalal]

"I think love to see more info in the fps display for debugging.. such as memory usuage , cpu and gpu load, and temp too, I feel this would help with tweaking settings for better performance ^.^"

We can achieve this using Mangohud.

We would need to change our Show FPS toggle to enable mangohud (env var MANGOHUD=1) with the correct settings.

Note that I don't think this will work in Glibc containers. Please confirm.