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/timerlayer/timerlayer.go

@@ -2014,10 +2014,10 @@ func (s *TimerLayerChannelStore) UpdateLastViewedAt(channelIds []string, userID
 	return result, err
 }
 
-func (s *TimerLayerChannelStore) UpdateLastViewedAtPost(unreadPost *model.Post, userID string, mentionCount int, mentionCountRoot int, updateThreads bool) (*model.ChannelUnreadAt, error) {
+func (s *TimerLayerChannelStore) UpdateLastViewedAtPost(unreadPost *model.Post, userID string, mentionCount int, mentionCountRoot int, updateThreads bool, setUnreadCountRoot bool) (*model.ChannelUnreadAt, error) {
 	start := timemodule.Now()
 
-	result, err := s.ChannelStore.UpdateLastViewedAtPost(unreadPost, userID, mentionCount, mentionCountRoot, updateThreads)
+	result, err := s.ChannelStore.UpdateLastViewedAtPost(unreadPost, userID, mentionCount, mentionCountRoot, updateThreads, setUnreadCountRoot)
 
 	elapsed := float64(timemodule.Since(start)) / float64(timemodule.Second)
 	if s.Root.Metrics != nil {
@@ -8054,6 +8054,22 @@ func (s *TimerLayerThreadStore) MarkAllAsRead(userID string, teamID string) erro
 	return err
 }
 
+func (s *TimerLayerThreadStore) MarkAllAsReadInChannels(userID string, channelIDs []string) error {
+	start := timemodule.Now()
+
+	err := s.ThreadStore.MarkAllAsReadInChannels(userID, channelIDs)
+
+	elapsed := float64(timemodule.Since(start)) / float64(timemodule.Second)
+	if s.Root.Metrics != nil {
+		success := "false"
+		if err == nil {
+			success = "true"
+		}
+		s.Root.Metrics.ObserveStoreMethodDuration("ThreadStore.MarkAllAsReadInChannels", success, elapsed)
+	}
+	return err
+}
+
 func (s *TimerLayerThreadStore) MarkAsRead(userID string, threadID string, timestamp int64) error {
 	start := timemodule.Now()