Add compatibility for S3-compatible services like OCI with path-style access support

[kyounghunJang]

I am currently using Oracle Cloud Object Storage (S3). Since embulk-output-s3 utilizes the AWS SDK, I initially expected it to be compatible without any issues.

However, Oracle S3 requires requests to be sent in the format: https://{namespace}.compat.objectstorage.{region}.oraclecloud.com/bucket. The current plugin, however, sends requests in the format bucket.namespace~~, which causes certificate authentication issues.

To work around this issue, I proposed adding a path_style_access option in the YAML configuration and suggested incorporating this option into the plugin. I also uploaded a related Pull Request (PR) for this improvement.

This change improves compatibility with Oracle Cloud Object Storage while maintaining the existing functionality. Looking forward to your feedback! 🚀