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/storetest/mocks/ThreadStore.go

@@ -263,6 +263,20 @@ func (_m *ThreadStore) MarkAllAsRead(userID string, teamID string) error {
 	return r0
 }
 
+// MarkAllAsReadInChannels provides a mock function with given fields: userID, channelIDs
+func (_m *ThreadStore) MarkAllAsReadInChannels(userID string, channelIDs []string) error {
+	ret := _m.Called(userID, channelIDs)
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(string, []string) error); ok {
+		r0 = rf(userID, channelIDs)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
 // MarkAsRead provides a mock function with given fields: userID, threadID, timestamp
 func (_m *ThreadStore) MarkAsRead(userID string, threadID string, timestamp int64) error {
 	ret := _m.Called(userID, threadID, timestamp)