Pure builder that attaches an asset to a STAC Item or Collection.
Assets set at creation time via new_item() can be complemented or
overwritten later with this function. No disk I/O is performed.
Arguments
- doc
A STAC document (
doc_itemordoc_collection).- key
A
charactername for the asset in the document'sassetsmap.- asset
A
listdescribing the asset, as fromnew_asset().
