docs(table): only expand the first row to save room in tree data example

Author: ronannnn

docs/app/components/content/examples/table/TableTreeDataExample.vue

@@ -137,14 +137,16 @@ const columns: TableColumn<Payment>[] = [{
     return h('div', { class: 'text-right font-medium' }, formatted)
   }
 }]
+
+const expanded = ref({ 0: true })
 </script>
 
 <template>
   <UTable
+    v-model:expanded="expanded"
     :data="data"
     :columns="columns"
     :get-sub-rows="row => row.children"
-    expanded
     sticky
     class="flex-1 h-96"
     :ui="{