drivers: Tune s3 uploader for better performance

Increase the concurrency and the part size so the uploads
are more performant in our production environment.

These are also more compatible with Storj's configuration
which saves files in 64MB chunks on the decentralized network,
so that part size also works well for them. But it still improves
upload performance to gcloud in around 10x as well.

drivers/s3.go

@@ -300,7 +300,8 @@ func (os *s3Session) saveDataPut(ctx context.Context, name string, data io.Reade
 	}
 
 	uploader := s3manager.NewUploader(os.s3sess, func(u *s3manager.Uploader) {
-		u.Concurrency = 2
+		u.Concurrency = 8
+		u.PartSize = 32 * 1024 * 1024
 		u.RequestOptions = append(u.RequestOptions, request.WithLogLevel(aws.LogDebug))
 	})
 	params := &s3manager.UploadInput{