Add custom metadata to ChatMessageContent like DateTimeCreated message was generated

[giannik]

What is the recommended way to add custom information to either the user or ai generated response like datetime created to show the actual time the message was logged in the chat history. This could also apply to any other custom metadata you may want to save

_chatHistory.Add(new ChatMessageContent() { Content = input, 
                Role = ChatMessageRole.User
                DateTimestamp = DateTime.UtcNow ??
                
            });;

[sophialagerkranspandey]

Tagging @markwallace-microsoft to reply once he returns from vacation.