feat: added render_order to the objects to control when they are sent to the gpu

[akowi-sknobloch]

When rendering 2D Scenes it's common to use the render order to control wich objects get rendered on top of each others.
I've added render_order to the Object struct to control this behaviour.
This works similar to the z-index in CSS where a higher render_order causes objects to be rendered in front.

[ElhamAryanpur]

@akowi-sknobloch you could already achieve it with z index directly tbh. As all scenes are 3D inherently, so just manipulating the z index could change their order regardless of the render order.

I'll still look into it and test it out, ty for the PR 🔥