MM-34758 Collapsed Reply Threads without mobile support (#17424)

Summary
added support for legacy clients accessing server
added collapsed_threads_supported param to viewChannel API and setPostUnread API

Ticket Link
https://mattermost.atlassian.net/browse/MM-34758

Related Webapp PR
mattermost/mattermost-webapp#7933

store/retrylayer/retrylayer.go

@@ -2308,11 +2308,11 @@ func (s *RetryLayerChannelStore) UpdateLastViewedAt(channelIds []string, userID
 
 }
 
-func (s *RetryLayerChannelStore) UpdateLastViewedAtPost(unreadPost *model.Post, userID string, mentionCount int, mentionCountRoot int, updateThreads bool) (*model.ChannelUnreadAt, error) {
+func (s *RetryLayerChannelStore) UpdateLastViewedAtPost(unreadPost *model.Post, userID string, mentionCount int, mentionCountRoot int, updateThreads bool, setUnreadCountRoot bool) (*model.ChannelUnreadAt, error) {
 
 	tries := 0
 	for {
-		result, err := s.ChannelStore.UpdateLastViewedAtPost(unreadPost, userID, mentionCount, mentionCountRoot, updateThreads)
+		result, err := s.ChannelStore.UpdateLastViewedAtPost(unreadPost, userID, mentionCount, mentionCountRoot, updateThreads, setUnreadCountRoot)
 		if err == nil {
 			return result, nil
 		}
@@ -9728,6 +9728,26 @@ func (s *RetryLayerThreadStore) MarkAllAsRead(userID string, teamID string) erro
 
 }
 
+func (s *RetryLayerThreadStore) MarkAllAsReadInChannels(userID string, channelIDs []string) error {
+
+	tries := 0
+	for {
+		err := s.ThreadStore.MarkAllAsReadInChannels(userID, channelIDs)
+		if err == nil {
+			return nil
+		}
+		if !isRepeatableError(err) {
+			return err
+		}
+		tries++
+		if tries >= 3 {
+			err = errors.Wrap(err, "giving up after 3 consecutive repeatable transaction failures")
+			return err
+		}
+	}
+
+}
+
 func (s *RetryLayerThreadStore) MarkAsRead(userID string, threadID string, timestamp int64) error {
 
 	tries := 0