[Feature][LastFM] Recommendations

[Schaka]

This issue serves as a milestone for LastFM integration.

• Let user know that LastFM needs to be set up in Navidrome for access to better recommendations
• Implement manual artist recommendations via getSimilar
• Implement manual track recommendations via getSimilar

This will likely not require saving LastFM metadata for our library. LastFM takes musicbrainz IDs for a lot of endpoints.
Additionally, recommendations are probably better suited to actually listened to songs and artists via Navidrome, not the entire library.

Recommendations do need to be matched against the existing database via musicbrainz id. If this isn't possible for everything (i.e. some data exists on LastFM but not Musicbrainz) additional data is required for our local database.