Import/Export quiz via JSON

This feature adds JSON-based import and export capabilities to the quiz plugin, enabling editors to efficiently create, transfer, and maintain quizzes outside the CMS. Quizzes, including their structure, questions, answers, and metadata, can be exported as JSON files and re-imported at any time. This allows for bulk editing, version control, reuse across environments, and easier collaboration between teams. The JSON format ensures a standardized, machine-readable representation of quiz content while preserving compatibility with existing quiz functionality.