[Feature][Spotify] Recommendations

[Schaka]

This issue serves as a milestone for Spotify integration.

• Set up Spotify access via universal (to Naviseerr) API key
• match local database to Spotify metadata, Musicbrainz should have an API for pulling this info via Spotify links, but we may need the reverse
• build 2-3 different approaches to recommendations (e.g. playlists, artists, library)

The hardest part will likely be matching metadata and keeping our local database up to date, so that no recommendations are given that the user is already aware of.