Agent replies are not recorded until the user speaks afterwards

[gcampax]

Because a turn starts with the agent and ends with the user (multiwoz-style), we don't store the turn until the user speaks. But that makes the log less useful for debugging, because any error or debugging info about the agent reply is not included.

We should store the turn immediately when the agent speaks, and then update the turn again when the user speaks. We can do that because we use a database now.