We want to extend the functionality of the itemBySitelink field so that it also accepts a sitelink URL (i.e. the URL of the wiki page the item links to) as a parameter instead of the siteId and title, e.g. itemBySitelink( url: "https://en.wikipedia.org/wiki/Potato" ) { id } should return the id Q10998.

Open questions:

• do we have to support all URL formats e.g. /w/index.php?title=Potato?
• what about mobile URLs?