Update available connections overview

[johnymontana]

• include curated connections at beginning of doc (where a detailed connection page is available)
• add top connections per category

[Copilot]

Pull Request Overview

This PR updates the available connections overview by adding curated connections at the beginning of the document and reorganizing content by category. The update expands the connection showcase from a simple Commerce section to a comprehensive overview featuring top connections across multiple categories.

• Adds curated connections with detailed pages at the beginning (Neo4j AuraDB, Supabase, MongoDB)
• Introduces new categorical sections: Artificial Intelligence, Business Management, CRM, and Communication
• Expands existing Commerce and Data & Analytics sections with additional connection cards