Avoid storing duplicate message id in ScaleoutStore

Currently for what reason when backplane receives duplicate message id,  the duplicate message id will be saved in ScaleoutStore and infinite duplicate messages could be sent to clients, as we discussed, to avoid duplicate messages, we change to not store duplicate message id in ScaleoutStore.
In the existing code, we create a new store when id < MaxMapping.Id, so we can also create a new store when id == MaxMapping.Id

Verified:
1). When a message id is duplicate, the message is not sent to clients


#2988