feat: add markitdown plugin

[Yevanchen]

• Add structured JSON response format - Include detailed conversion status for each file - Maintain backward compatibility - Improve error handling and status reporting

This PR adds JSON response support to the markitdown plugin, enhancing its functionality and integration capabilities.

Changes:

• Add structured JSON response format for better data handling
• Include detailed conversion status for each processed file
• Maintain backward compatibility with existing text and blob responses
• Improve error handling and status reporting

The JSON response structure includes:

• Overall conversion status
• Total files processed
• Number of successful conversions
• Detailed results for each file including:
  • Filename
  • Conversion status
  • Converted content (if successful)
  • Error message (if failed)

Plugin Submission Form

1. Submission Type

• New plugin submission
• Version update for existing plugin

2. Description

The Markitdown plugin is a powerful document conversion tool that transforms various file formats into well-formatted Markdown. It provides multiple response formats including text, blob, and structured JSON, making it highly versatile for different use cases. The plugin supports batch processing of multiple files and provides detailed conversion status and results.

Key features:

• Multiple file format support
• Structured JSON response format
• Detailed conversion status tracking
• Error handling and reporting
• Batch processing capabilities

3. Checklist

• I have read and followed the Publish to Dify Marketplace guidelines
• I have read and comply with the Plugin Developer Agreement
• I confirm my plugin works properly on both Dify Community Edition and Cloud Version
• I confirm my plugin has been thoroughly tested for completeness and functionality
• My plugin brings new value to Dify

4. Documentation Checklist

Please confirm that your plugin README includes all necessary information:

• Step-by-step setup instructions
• Detailed usage instructions
• All required APIs and credentials are clearly listed
• Connection requirements and configuration details

5. Privacy Protection Information

Based on Dify Plugin Privacy Protection Guidelines:

Data Collection

The Markitdown plugin does not collect any personal user data. It only processes the files that users explicitly provide for conversion. The plugin:

• Does not store any user files permanently
• Uses temporary storage only during conversion process
• Does not collect any user metadata or personal information
• Does not track usage patterns or user behavior
• Does not require any user authentication or personal credentials

Privacy Policy

• I confirm that I have prepared and included a privacy policy in my plugin package based on the Plugin Privacy Protection Guidelines