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

scheduler/log_adapter.go

@@ -0,0 +1,24 @@
+package scheduler
+
+import (
+	"github.com/navidrome/navidrome/log"
+)
+
+type logger struct{}
+
+func (l *logger) Info(msg string, keysAndValues ...interface{}) {
+	args := []interface{}{
+		"Scheduler: " + msg,
+	}
+	args = append(args, keysAndValues...)
+	log.Debug(args...)
+}
+
+func (l *logger) Error(err error, msg string, keysAndValues ...interface{}) {
+	args := []interface{}{
+		"Scheduler: " + msg,
+	}
+	args = append(args, keysAndValues...)
+	args = append(args, err)
+	log.Error(args...)
+}