Improve MIME type detection for image URLs

[Seayon]

Implement fallback to content-based detection using Pillow when URL-based guess fails, enhancing accuracy while maintaining efficiency.

Checklist:

Important

Please review the checklist below before submitting your pull request.

• Please open an issue before creating a PR or link to an existing issue
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

Description

Describe the big picture of your changes here to communicate to the maintainers why we should accept this pull request. If it fixes a bug or resolves a feature request, be sure to link to that issue. Close issue syntax: Fixes #<issue number>, see documentation for more details.

Fixes #6529

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update, included: Dify Document
• Improvement, including but not limited to code refactoring, performance optimization, and UI/UX improvement
• Dependency upgrade

Testing Instructions

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• I uploaded an image to Aliyun OSS that was actually in JPEG format but had a PNG file extension. When I tried to use Anthropic's LLM for image recognition, it resulted in an error.
  After making the modifications, I used the same image again, and the API call was successful. Everything worked normally.
• Test B

[laipz8200]

Hello @Seayon, sorry for replying so late, could you please sync your branch with the main branch first? I think this PR could be merged.

[Seayon]

Hello @Seayon, sorry for replying so late, could you please sync your branch with the main branch first? I think this PR could be merged.

Hello @laipz8200

Thank you for your review. I've synced the branch with the main branch and performed some cleanup. The branch should now be up-to-date, and the commits are clean. I look forward to your approval for merging this PR.

Let me know if you need any further information or changes.

[laipz8200]

Thanks!