Feat: AWS S3 support

[I-Info]

Sweep Summary

Adds AWS S3 object storage support to FastGPT as an alternative file storage option for chat files.

• Implemented S3 client integration in packages/service/common/file/s3/index.ts using Minio library for bucket operations and presigned URL generation.
• Created a new API endpoint in projects/app/src/pages/api/common/file/s3PresignedUpload.ts to handle S3 presigned URL generation with proper authentication.
• Modified the file upload controller in projects/app/src/web/common/file/controller.ts to use S3 for chat files while keeping MongoDB GridFS for dataset files.
• Added S3 configuration parameters to .env.template and updated system initialization to verify S3 bucket existence on startup.

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