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

app/post.go

@@ -88,7 +88,7 @@ func (a *App) CreatePostAsUser(c *request.Context, post *model.Post, currentSess
 	_, fromWebhook := post.GetProps()["from_webhook"]
 	_, fromBot := post.GetProps()["from_bot"]
 	if !fromWebhook && !fromBot {
-		if _, err := a.MarkChannelsAsViewed([]string{post.ChannelId}, post.UserId, currentSessionId); err != nil {
+		if _, err := a.MarkChannelsAsViewed([]string{post.ChannelId}, post.UserId, currentSessionId, true); err != nil {
 			mlog.Warn(
 				"Encountered error updating last viewed",
 				mlog.String("channel_id", post.ChannelId),