Listenbrainz scrobbling (#1424)

* Refactor session_keys to its own package

* Adjust play_tracker

- Don't send external NowPlaying/Scrobble for tracks with unknown artist
- Continue to the next agent on error

* Implement ListenBrainz Agent and Auth Router

* Implement frontend for ListenBrainz linking

* Update listenBrainzRequest

- Don't marshal Player to json
- Rename Track to Title

* Return ErrRetryLater on ListenBrainz server errors

* Add tests for listenBrainzAgent

* Add tests for ListenBrainz Client

* Adjust ListenBrainzTokenDialog to handle errors better

* Refactor listenbrainz.formatListen and listenBrainzRequest structs

* Refactor agent auth_routers

* Refactor session_keys to agents package

* Add test for listenBrainzResponse

* Add tests for ListenBrainz auth_router

* Update ListenBrainzTokenDialog and auth_router

* Adjust player scrobble toggle

tests/fixtures/listenbrainz.nowplaying.request.json

@@ -0,0 +1 @@
+ {"listen_type": "playing_now", "payload": [{"track_metadata": { "artist_name": "Track Artist", "track_name": "Track Title", "release_name": "Track Album", "additional_info": { "tracknumber": 1, "track_mbid": "mbz-123", "artist_mbids": ["mbz-789"], "release_mbid": "mbz-456"}}}]}

tests/fixtures/listenbrainz.scrobble.request.json

@@ -0,0 +1 @@
+ {"listen_type": "single", "payload": [{"listened_at": 1635000000, "track_metadata": { "artist_name": "Track Artist", "track_name": "Track Title", "release_name": "Track Album", "additional_info": { "tracknumber": 1, "track_mbid": "mbz-123", "artist_mbids": ["mbz-789"], "release_mbid": "mbz-456"}}}]}