[MM-41998] Channel Info RHS: display number of files for a channel (#19822)

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

store/timerlayer/timerlayer.go

@@ -1157,6 +1157,22 @@ func (s *TimerLayerChannelStore) GetDeletedByName(team_id string, name string) (
 	return result, err
 }
 
+func (s *TimerLayerChannelStore) GetFileCount(channelID string) (int64, error) {
+	start := timemodule.Now()
+
+	result, err := s.ChannelStore.GetFileCount(channelID)
+
+	elapsed := float64(timemodule.Since(start)) / float64(timemodule.Second)
+	if s.Root.Metrics != nil {
+		success := "false"
+		if err == nil {
+			success = "true"
+		}
+		s.Root.Metrics.ObserveStoreMethodDuration("ChannelStore.GetFileCount", success, elapsed)
+	}
+	return result, err
+}
+
 func (s *TimerLayerChannelStore) GetForPost(postID string) (*model.Channel, error) {
 	start := timemodule.Now()