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

core/agents/session_keys.go

@@ -0,0 +1,25 @@
+package agents
+
+import (
+	"context"
+
+	"github.com/navidrome/navidrome/model"
+)
+
+// SessionKeys is a simple wrapper around the UserPropsRepository
+type SessionKeys struct {
+	model.DataStore
+	KeyName string
+}
+
+func (sk *SessionKeys) Put(ctx context.Context, userId, sessionKey string) error {
+	return sk.DataStore.UserProps(ctx).Put(userId, sk.KeyName, sessionKey)
+}
+
+func (sk *SessionKeys) Get(ctx context.Context, userId string) (string, error) {
+	return sk.DataStore.UserProps(ctx).Get(userId, sk.KeyName)
+}
+
+func (sk *SessionKeys) Delete(ctx context.Context, userId string) error {
+	return sk.DataStore.UserProps(ctx).Delete(userId, sk.KeyName)
+}