ENGCOM-4333: Issue Fixed #21322 : Declarative schema: Omitting indexType throws exception #21328

 - Merge Pull Request #21328 from cedcommerce/magento2:issue-fix-21322-2.3-develop
 - Merged commits:
   1. b179e54

Author: magento-engcom-team

lib/internal/Magento/Framework/Setup/Declaration/Schema/Dto/Factories/Index.php

@@ -19,7 +19,7 @@ class Index implements FactoryInterface
     /**
      * Default index type.
      */
-    const DEFAULT_INDEX_TYPE = "BTREE";
+    const DEFAULT_INDEX_TYPE = "btree";
 
     /**
      * @var ObjectManagerInterface