[R2] Update Presigned URL docs

[harshil1712]

Summary

Clarifies Presigned URLs in R2. Fixes #19190

Documentation checklist

• The documentation style guide has been adhered to.

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PR Change Summary

Updated documentation for Presigned URLs in R2 to clarify usage and examples.

• Clarified the generation and usage of presigned URLs in R2 documentation.
• Added an example of generating presigned URLs using the aws4fetch package.
• Updated the explanation of differences between presigned URLs and R2 bindings.

Modified Files

• src/content/docs/r2/api/s3/presigned-urls.mdx

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[github-actions]

Preview URL: https://f57dc42d.preview.developers.cloudflare.com
Preview Branch URL: https://r2-fix-presigned-url.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/r2/api/s3/presigned-urls/	https://r2-fix-presigned-url.preview.developers.cloudflare.com/r2/api/s3/presigned-urls/