Turn on edit mode for product repository when adding children

This should fix the issue with the configurable products not having any options with Bulk and Async API.
Related issue: #20366

app/code/Magento/ConfigurableProduct/Model/LinkManagement.php

@@ -110,7 +110,7 @@ public function getChildren($sku)
      */
     public function addChild($sku, $childSku)
     {
-        $product = $this->productRepository->get($sku);
+        $product = $this->productRepository->get($sku, true);
         $child = $this->productRepository->get($childSku);
 
         $childrenIds = array_values($this->configurableType->getChildrenIds($product->getId())[0]);