feat(image-downloader): add new image downloader plugin

[lzfxxx]

Plugin Submission Form

1. Metadata

• Plugin Author: lzfxxx
• Plugin Name: image-downloader
• Repository URL: https://github.com/lzfxxx/image-downloader

2. Submission Type

• New plugin submission
• Version update for existing plugin

3. Description

This plugin downloads images from URLs and returns them as blobs. It solves the CSP (Content Security Policy) restriction issue in Dify cloud version (udify.app) where external images can't be displayed. When AI generates markdown text with image references to external domains, this plugin downloads the images and serves them through blob URLs, bypassing CSP restrictions.

4. 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

5. 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
• Link to the repository for the plugin source code

6. Privacy Protection Information

Based on Dify Plugin Privacy Protection Guidelines:

Data Collection

No, this plugin does not collect any user personal data. It only downloads image files from the provided URLs.

Privacy Policy

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

[LogicOber]

Thank you so much for your pull request on GitHub! 😊 Your contributions are greatly appreciated!

Please ensure that:

• All content in PRIVACY.md, README.md, and 👉 code remains in English only 👈 (e.g., when you use yield self.create_text_message)
• Please ensure that the label for different languages in the YAML file are written in their corresponding languages.

Looking forward to your updates! 💯

[lzfxxx]

@LogicOber updated