feat(sunshine): add Prism Launcher (Minecraft)

[gabbelitoV2]

Summary

Adds Prism Launcher (Minecraft) to the Sunshine container.

Changes

• Download and install Prism Launcher AppImage
• Add Java 21 and Qt6 dependencies
• Add Prism Launcher to Sunshine apps.json
• Add Prism Launcher to XFCE4 panel (taskbar)
• Install icons to system icon theme (all sizes)
• Add start/stop scripts

Testing

• Verified Prism Launcher starts correctly
• Verified icon shows in XFCE4 panel
• Verified icon shows in Sunshine/Moonlight

[PierreBeucher]

Hi there ! Thanks again for this contribution. Adding this launcher is great, though I fear our base image would become too gid. What would be nice is to add the ability to add this launcher on-demand after initial setup: a simple command or button to click and it would install everything, using most of the code you have here.

It's also an overall design decision for how to add launchers on-the-fly. I'll try to think of something ASAP