Need some way to nest labeled assets

## Bevy version

0.16-dev after https://github.com/bevyengine/bevy/pull/15481

## Overview

If you have an asset that loads nested glTFs, for example my `bevy-glxf-loader`, then if you have more than one glTF in that asset the names like `Scene0`, `Mesh0`, etc. will collide. What I'd like is to be able to namespace those loaded assets with a prefix of some kind.