Change scope to include STAC Collections

[amsnyder]

We would like to apply this extension to STAC Collections. We are converting model outputs to zarr stores, and cataloging these zarr stores as STAC collections, rather than items. Is there any reason the scope of this extension cannot be applied to a STAC Collection?

[rhysrevans3]

Sorry for the very late reply. I've update the schema to now be used for Items or Collections