Docs: add S3 persistent storage configuration

[aki366]

✨ Summary

I am planning to add documentation on setting up the use of the cloud as persistent storage for Dify, which seems to be in demand.
I will add multilingual documentation using AWS S3 as an example.

This document explains how to switch from local storage (/app/api/storage) to AWS S3 using environment variables in the Kubernetes manifest.

It is written in Japanese, English, and Chinese to support a wider range of users and contributors.

Changes

• Added multilingual section to README:
  • Use S3 for storing uploaded files (PDF, CSV, etc.).
  • Set required environment variables in api.yaml and worker.yaml.
  • Use Kubernetes Secrets to securely reference credentials
• Include a link to the official documentation.

💬 Notes.

We would like to add documentation on storage configuration.

I have created a README under dify/api/ as a section close to the code, but it would be helpful if you could review if this policy is acceptable!

[Winson-030]

Thanks for your great contribution Aki san. I will review ASAP.