Introduce Audience Insights Agent and Reporting Tool

Add a third `AssistantAgent` called 'Audience Insights Specialist' to your `GroupChat`. This agent should have a tool `query_audience_metrics(content_type, time_period)` that simulates fetching audience engagement metrics. Also, create a `reporting_tool(title, content)` function that agents can use to finalize their recommendation into a structured markdown output. Ensure the agents understand how to collaborate and use each other's tools.