Missing uri in SearchResult

[sapristi]

Hello,
it seems that search results are missing the uri field. It's not yet mandatory, but may soon be, see mopidy/mopidy#2190

I checked if it would be possible to add directly, taking inspiration from mopidy local ( https://github.com/mopidy/mopidy-local/blob/main/src/mopidy_local/library.py#L98), but it's not fully straigthforward - would require moving the handling of query to the search function.