add root span for weekly reminder

cmd/themis-server/main.go

@@ -732,6 +732,12 @@ func main() {
 	log.Info().Int("count", len(created)).Dur("startup_latency_ms", time.Since(start)).Msg("registered commands, ready to operate")
 
 	go notifier.NotifyFunc(ctx, func() {
+		ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
+		defer cancel()
+
+		ctx, span := tracer.Start(ctx, "weekly notification", trace.WithNewRoot())
+		defer span.End()
+
 		log.Info().Msg("sending weekly reminder")
 		absentees, err := store.GetAbsentees(ctx, themis.NextMonday())
 		if err != nil {