This is a partial reboot of STYLE-79 and https://wiki.musicbrainz.org/User:Hrglgrmpf/CD_Baby_Relationship_Type. We have "purchase for mail-order" and "purchase for download" URL relationships for the release level, but on the Artist level we have both "purchase music for mail-order" and "purchase music for download." The problem with this is CD Baby sells both physical CDs for mail-order and digital downloads, so editors are left wondering if they should choose between the two or re-enter the same URL using both relationships. A good solution to this problem would be to implement an artist-level "has CD Baby at" relationship similar to what we have for Bandcamp URLs.