Register imagePullThroughput and count with MiB

Signed-off-by: Shukui Yang <yangshukui@bytedance.com>

pkg/cri/server/image_pull.go

@@ -209,8 +209,9 @@ func (c *criService) PullImage(ctx context.Context, r *runtime.PullImageRequest)
 		}
 	}
 
+	const mbToByte = 1024 * 1024
 	size, _ := image.Size(ctx)
-	imagePullingSpeed := float64(size) / time.Since(startTime).Seconds()
+	imagePullingSpeed := float64(size) / mbToByte / time.Since(startTime).Seconds()
 	imagePullThroughput.Observe(imagePullingSpeed)
 
 	log.G(ctx).Infof("Pulled image %q with image id %q, repo tag %q, repo digest %q, size %q in %s", imageRef, imageID,