Extending AssetCatalogueProvider::storeAsset() To Accept File Streams/Strings

Following a discussion with @acuthbert, we've identified a use case where passing a file Stream or a String (to be written to a file) to `storeAsset()` would be worthwhile.

Currently, if a file is being generated by another process, we have to store it in a temporary location first, before passing it to `storeAsset()`. This feature addition would remove that requirement.