Add User Authentication to GSSoC Leaderboard Dashboard

[Sharmeen20]

Enhance the GSSoC Leaderboard dashboard by implementing user authentication using the streamlit-authenticator package. This will ensure that only authorized users can access the dashboard, improving security and enabling user-specific features in the future.

Changes proposed:

• Add user login functionality to the main dashboard.
• Implement role-based access control if necessary.
• Include user session management with cookie expiration settings.

Please assign this to me.

[github-actions]

Welcome @Sharmeen20! 🎉 Thank you for your first contribution to this project. We're excited to have you on board!