fix: highlight missing code block in OpenSearch integration doc

Author: Yono1112

src/pages/[platform]/build-a-backend/data/custom-business-logic/search-and-aggregate-queries/index.mdx

@@ -142,6 +142,7 @@ const tableArn = backend.data.resources.tables['Todo'].tableArn;
 // Get the DynamoDB table name
 const tableName = backend.data.resources.tables['Todo'].tableName;
 
+// highlight-start
 // Create the OpenSearch domain
 const openSearchDomain = new opensearch.Domain(
   backend.data.stack,