Point cloud test model?

One of the important use cases of glTF I've seen that doesn't seem to be covered in this repository are point clouds.

glTF-Sample-Models had MeshPrimitiveTest but I'm not really suggesting including that one - it feels like we should have some test instead that is a more realistic/heavy-weight test of point clouds specifically.

Sketchfab has a lot of assets that are point cloud scans but I'm not sure what the licensing restrictions here are. I'm thinking of something along these lines: https://sketchfab.com/3d-models/flower-point-cloud-photogrammetry-13a409d10f154d5dbfd009fe75d52222

Review the existing glTF-Sample-Models test assets and the repository's contribution and licensing expectations first. Then investigate the linked Sketchfab point-cloud asset and alternatives, and confirm that a realistic, heavyweight point-cloud sample can be legally included; done means an approved asset is added to the sample collection.

Written by the indexing model from the issue text.