refactor: Refactor S3 configuration structure and fix Python 3.9 compatibility issues

[baojun-zhang]

Description

Refactor S3 configuration structure and fix Python 3.9 compatibility issues

Related Issue

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Extract S3-related configurations from AGFSConfig into a new S3Config class
• Update agfs_manager.py to use the new S3Config structure
• Modify test_config_validation.py to adapt to the new configuration structure
• Update configuration example files to reflect the new configuration structure
• Fix Python 3.9 compatibility issue in embedding_queue.py by replacing EmbeddingMsg | None with Optional[EmbeddingMsg]

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Additional Notes

ov.conf example

{
  # .....
  "storage": {
    "agfs": {
      "port": 8080,
      "log_level": "warn",
      "path": "./data",
      "backend": "s3",
      "url": "http://localhost:8080",
      "timeout": 10,
      "retry_times": 3,
      "s3": {
        "bucket": "openviking-test",
        "endpoint": "http://127.0.0.1:8333",
        "region": "us-east-1",
        "access_key": "any",
        "secret_key": "any",
        "prefix": "",
        "use_ssl": "false"
      }
    }
  }
}