Update the conversation status as closed

[Oceania2018]

A Conversation Hook needs to be implemented to update Conversation to the closed state.

The conversation will be closed in two situations:

• When the conversation ends normally and is triggered by LLM,;
• When the idle time is exceeded and the conversation is forcibly ended by the background;

No matter which situation is triggered, the OnConversationEnding method in IConversationHook will be called.

Therefore we can implement a new conversation hook here and update the conversation status to ConversationStatus.Closed in the OnConversationEnding function.

[wilson-dixon]

@Oceania2018 was this implemented?

[Oceania2018]

@waelhosn I think it's been implemented from this PR. Let me know if it's working or not.