Improvements in the Meeting Prep sample

[jsuarezruiz]

Changes:

• Fix issue invoking functions by auto function calls.
• Fix issue in the fetch_event_details method with pending parameters.
• Updated the sample README to include more details like a troubleshooting section, providing guidance on common errors and resolution steps.
• After some iteration added a more detailed system instructions to the agent, ensuring greater accuracy, contextual awareness, and better guidance for responses.