Address issue #4882 by adding album barcode as a new import disambiguator

[Sean-T-Moore]

Description

This PR addresses issue #4882 by adding barcode as a new import disambiguator. Currently it can be difficult to distinguish and select the proper album release during beets import. Musicbrainz considers an album to be a distinct release if it differs by media-type, country, year, label, catalog-number or barcode. Beets has been using all these parameters except barcode to disambiguate the releases. It is often the case that a catalog item is released for sale via stores with a barcode and via other channels (e.g. club memberships) without a barcode. The changes made as part of this PR allow the user to distinguish between these variants and select the correct release during import.

Changes include:

• adding barcode as an AlbumInfo field
• populating barcode from MusicBrainz API release data
• using barcode during the candidate distance calculation as a new disambiguator
• updating documentation to show barcode as a new disambiguator

To Do

• [x] Documentation. (If you've add a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• [x] Changelog. (Add an entry to docs/changelog.rst near the top of the document.)
• [ ] Tests. (Encouraged but not strictly required.)

[stale[bot]]

Is this still relevant? If so, what is blocking it? Is there anything you can do to help move it forward?

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[Sean-T-Moore]

This PR was ready to be merged on the date it was submitted. Perhaps a maintainer can comment on why it wasn't merged then before I do any more work to resolve new conflicts.