feat: add support for X-Forwarded-Port in ProxyFix middleware

[osaimi]

Summary

Updated ProxyFix middleware to include x_port=1 for handling the X-Forwarded-Port header. Improved the description of RESPECT_XFORWARD_HEADERS_ENABLED for clarity.

I couldn't find RESPECT_XFORWARD_HEADERS_ENABLED in the Dify Document. Please advise if documentation should be added.

Fixes #13070

Screenshots

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Checklist

• 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