PB-390: Nested Page Builder content can fail to save when action is performed quickly

- Add db schema white list

Author: davemacaulay

app/code/Magento/PageBuilder/etc/db_schema_whitelist.json

@@ -0,0 +1,24 @@
+{
+    "catalog_eav_attribute": {
+        "column": {
+            "is_pagebuilder_enabled": true
+        }
+    },
+    "pagebuilder_template": {
+        "column": {
+            "template_id": true,
+            "name": true,
+            "preview_image": true,
+            "template": true,
+            "created_for": true,
+            "created_at": true,
+            "updated_at": true
+        },
+        "index": {
+            "PAGEBUILDER_TEMPLATE_NAME": true
+        },
+        "constraint": {
+            "PRIMARY": true
+        }
+    }
+}