Asset Idea: Create assets demonstrating the relationship between instancing and composition arcs

[mati-nvidia]

We were recently confused again by the expected behavior for instancing described in this thread: https://groups.google.com/g/usd-interest/c/_jOq0wqeR_8/m/TjOETa6QCQAJ

We should create an asset that exhibits the "issue" described in the thread (An attachment is already provided in the google group) and document the behavior. It would be good to also include an example of setting instanceable=true on the aggregation side of an asset reference to show the working case.