while it is against the bevy way, in an effort to reduce demo repeat code and increase example consistency:

• add shared example/harness/... crate
• consolidates camera control behaviors (e.g. switchable between PanOrbit, editor camera, fly camera, etc.)
• bevy inspector gui resource registration utility (for demos that benefit from UI sliders, color pickers, etc.)
• gaussian asset loading utilities, e.g. support for custom ply loads, common CDN asset urls, etc.