[SNS logger][New event property] Catch a session closed event with property 'df_bot'

[ear-dev]

There are some conversation flows where the session is closed by the bot. No appName/token being one. Another one is where the flow just comes to a natural conclusion and the visitor has no more questions.

We must be getting a flag from DF to close the session, and we should catch that in a new event.

let's make it this: {"close_method": "df_bot"} <- ?? - maybe DF.app?

[ear-dev]

@bhardwajaditya it looks like this event is catching more than just when we get the df_close_chat action payload from DF. I think it is also catching agentUnassigned, and maybe timeout? https://github.com/WideChat/Apps.Dialogflow/blob/master/handler/OnAgentUnassignedHandler.ts#L34

If we could find the spot where we exactly receive and parse the df_close_chat action, that would be more precise?

Can you take another look please? thanks...