chore: add copy example for expected bucket owner

src/pages/[platform]/build-a-backend/storage/copy-files/index.mdx

@@ -86,7 +86,8 @@ const copyFile = async () => {
         path: 'album/2024/1.jpg',
         // Specify a target bucket using name assigned in Amplify Backend
         // or bucket name from console and associated region
-        bucket: 'assignedNameInAmplifyBackend'
+        bucket: 'assignedNameInAmplifyBackend',
+        expectedBucketOwner: '123456789012'
       },
       destination: {
         path: 'shared/2024/1.jpg',
@@ -95,7 +96,8 @@ const copyFile = async () => {
         bucket: {
           bucketName: 'generated-second-bucket-name',
           region: 'us-east-2'
-        }
+        },
+        expectedBucketOwner: '123456789013'
       }
     });
   } catch (error) {
@@ -116,7 +118,7 @@ Option | Type | Default | Description |
 | bucket | string \| <br />\{ bucketName: string;<br/> region: string; \} | Default bucket and region from Amplify configuration | A string representing the target bucket's assigned name in Amplify Backend or an object specifying the bucket name and region from the console.<br/><br/>Read more at [Configure additional storage buckets](/[platform]/build-a-backend/storage/set-up-storage/#configure-additional-storage-buckets). |
 | eTag | string | Optional | The copy **source object** entity tag (ETag) value. Only Copies the object if its ETag matches the specified tag. |
 | notModifiedSince | Date | Optional | Copies the **source object** if it hasn't been modified since the specified time.  <br /><br/> **This is evaluated only when `eTag` is NOT supplied**|
-| expectedBucketOwner | string | Optional | The account ID that owns source or destination bucket. |
+| expectedBucketOwner | string | Optional | `source.expectedBucketOwner`: The account ID that owns the source bucket. <br /><br /> `destination.expectedBucketOwner`: The account ID that owns the destination bucket. |
 
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