B2B-2469: Improve category children loading

- position fix in performance test fixtures

Author: rganin

setup/src/Magento/Setup/Fixtures/CategoriesFixture.php

@@ -135,6 +135,7 @@ private function generateCategories(
                     ->setName($this->getCategoryName($parentCategory, $nestingLevel, $i))
                     ->setParentId($parentCategory->getId())
                     ->setLevel($parentCategory->getLevel() + 1)
+                    ->setPosition($i)
                     ->setAvailableSortBy('name')
                     ->setIsAnchor($nestingLevel <= 2)
                     ->setDefaultSortBy('name')