AWS S3 storage provider.
Stores files in Amazon S3 buckets using the ExAWS library. Supports all S3-compatible services (like Backblaze B2, Cloudflare R2, Tigris).
Files under 5 MB are uploaded via put_object (single request).
Files at or above 5 MB use multipart upload via ExAws.S3.upload/4
with streaming and concurrent chunk uploads.