add support for Bandcamp release labels

[UltimateRiff]

some Bandcamp releases are attached to Bandcamp Labels (a different account type from Bandcamp artists). for example, this AFI release from Fantasy Records (see the link in the top left on desktop)

https://afiofficial.bandcamp.com/album/afi-the-blood-album

(the MusicBrainz logos in the screenshot come from the Bandcamp importer userscript)

[phw]

The label info is actually in the embedded JSON data as recordLabel, see https://validator.schema.org/#url=https%3A%2F%2Fafiofficial.bandcamp.com%2Falbum%2Fafi-the-blood-album