Use Dedicated GPU flag for Linux

[Wyvest]

prism sets the following environment variables:

DRI_PRIME=1
__NV_PRIME_RENDER_OFFLOAD=1
__VK_LAYER_NV_optimus=NVIDIA_only
__GLX_VENDOR_LIBRARY_NAME=nvidia

[lunaynx]

It also tries to do something with Switcheroo first: https://github.com/PrismLauncher/PrismLauncher/blob/d10acdb032fd88b203e080012e1bf6316eb88fcb/launcher/minecraft/MinecraftInstance.cpp#L110