[Proposal] Allow manually setting LODs similar to Unitys LOD groups

[xxSeys1]

Issue description:

Currently there is no way (I know of) to manually set meshes for LODs.

I'm requesting this feature because I'm generating tree with a tree generator software which spits out LODs that are better than the ones flax can generate because the tree is generated proceduraly and can be meshed at a lower density. But I need some way to get these LODs into flax.

There is a workaround for this by setting the LODs in Blender and exporting as fbx but that's a weird workaround and pulling every model through blender is not ideal at all.

Steps to reproduce:

Try to set a mesh as an lod of another model.

Minimal reproduction project:

none

Flax version:

1.8.1