add Listenbrainz account linking for External Connections integration

[dozro]

migrated from 7w1/sable#265

Description

inspiration from the functionality that sharkey has, but with opt-in bc it will establish a connection with an external server, so that should be behind a opt-in

still in it's early stages tho

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings