Breaking change: Add ScanSchedule, allows interval and cron based configurations.

See https://pkg.go.dev/github.com/robfig/cron#hdr-CRON_Expression_Format for expression syntax.

`ScanInterval` will still work for the time being. The only situation it does not work is when you want to disable periodic scanning by setting `ScanInterval=0`. If you want to disable it, please set `ScanSchedule=""`

Closes #1085

cmd/wire_injectors.go

@@ -9,6 +9,7 @@ import (
 	"github.com/navidrome/navidrome/core"
 	"github.com/navidrome/navidrome/persistence"
 	"github.com/navidrome/navidrome/scanner"
+	"github.com/navidrome/navidrome/scheduler"
 	"github.com/navidrome/navidrome/server"
 	"github.com/navidrome/navidrome/server/app"
 	"github.com/navidrome/navidrome/server/events"
@@ -82,3 +83,22 @@ func createBroker() events.Broker {
 		events.NewBroker,
 	))
 }
+
+// Scheduler must be a Singleton
+var (
+	onceScheduler     sync.Once
+	schedulerInstance scheduler.Scheduler
+)
+
+func GetScheduler() scheduler.Scheduler {
+	onceScheduler.Do(func() {
+		schedulerInstance = createScheduler()
+	})
+	return schedulerInstance
+}
+
+func createScheduler() scheduler.Scheduler {
+	panic(wire.Build(
+		scheduler.New,
+	))
+}