feat: Upload a folder to knowledgebase

[Silow9]

Summary

Made modification to make the system support uploading a folder so that the system recursively retrieves all files within the folder and sequentially adds them to the upload list. Add a button to upload the folder.
Remember to modify the Knowledge Configuration and NGINX_CLIENT_MAX_BODY_SIZE in the file named .env.example in main menu to ensure the uploading is allowed for size limitation.
This function requires the Web Browser supporting HTMLInputElement.webkitdirectory. Currently supported in Chrome, Firefox and Edge.

Fixes: #14240 (comment)

Screenshots

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Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods