[FEATURE] Configure hostname based requests for S3

[zachspar]

Right now, s3.rs is hard-coding path style requests with the S3 client. Not all storage providers accept this, and we should make it configurable in the toml file.

2026-02-09T22:34:50.663581Z ERROR attic_server::error: Storage error: Storage error: service error: unhandled error (PathStyleRequestNotAllowed): Error { code: "PathStyleRequestNotAllowed", message: "The path style requests are not allowed for this method, please switch to hostname-based requests.", aws_request_id: "fae25141-6bd3-91d8-bb0e-ca4171f348af" }