azure/s3 gateways: Pass ETag during GET call to avoid data corruption (#11024)

Both Azure & S3 gateways call for object information before returning
the stream of the object, however, the object content/length could be
modified meanwhile, which means it can return a corrupted object.

Use ETag to ensure that the object was not modified during the GET call

cmd/gateway/s3/gateway-s3.go

@@ -431,6 +431,11 @@ func (l *s3Objects) GetObject(ctx context.Context, bucket string, key string, st
 			return minio.ErrorRespToObjectError(err, bucket, key)
 		}
 	}
+
+	if etag != "" {
+		opts.SetMatchETag(etag)
+	}
+
 	object, _, _, err := l.Client.GetObject(ctx, bucket, key, opts)
 	if err != nil {
 		return minio.ErrorRespToObjectError(err, bucket, key)