Fix custom placeholders preview not showing external props

Author: synzen

services/backend-api/client/src/features/feedConnections/components/CustomPlaceholdersTabSection/CustomPlaceholderPreview.tsx

@@ -90,6 +90,7 @@ export const CustomPlaceholderPreview = ({
           formatTables: articleFormatOptions.formatTables,
           stripImages: articleFormatOptions.stripImages,
         },
+        externalProperties: articleFormatOptions.externalProperties,
       },
     },
   };