docs(VerticalNavigation): add slots examples (#456)

Co-authored-by: Benjamin Canac <canacb1@gmail.com>

docs/components/content/examples/VerticalNavigationExampleDefaultSlot.vue

@@ -0,0 +1,31 @@
+<script setup>
+const links = [{
+  label: 'Navigation',
+  children: [{
+    label: 'Vertical Navigation',
+    to: '/navigation/vertical-navigation'
+  }, {
+    label: 'Command Palette',
+    to: '/navigation/command-palette'
+  }]
+}, {
+  label: 'Data',
+  children: [{
+    label: 'Table',
+    to: '/data/table'
+  }]
+}]
+</script>
+
+<template>
+  <UVerticalNavigation :links="links">
+    <template #default="{ link }">
+      <div class="relative text-left w-full">
+        <div class="mb-2">
+          {{ link.label }}
+        </div>
+        <UVerticalNavigation v-if="link.children" :links="link.children" />
+      </div>
+    </template>
+  </UVerticalNavigation>
+</template>