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

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

store/retrylayer/retrylayer.go

@@ -1402,6 +1402,27 @@ func (s *RetryLayerChannelStore) GetDeletedByName(team_id string, name string) (
 
 }
 
+func (s *RetryLayerChannelStore) GetFileCount(channelID string) (int64, error) {
+
+	tries := 0
+	for {
+		result, err := s.ChannelStore.GetFileCount(channelID)
+		if err == nil {
+			return result, nil
+		}
+		if !isRepeatableError(err) {
+			return result, err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return result, err
+		}
+		timepkg.Sleep(100 * timepkg.Millisecond)
+	}
+
+}
+
 func (s *RetryLayerChannelStore) GetForPost(postID string) (*model.Channel, error) {
 
 	tries := 0