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

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

docs/components/content/examples/VerticalNavigationExampleIconSlot.vue

@@ -0,0 +1,41 @@
+<script setup>
+const types = {
+  bug: {
+    icon: 'i-heroicons-bug-ant-20-solid',
+    color: 'text-red-500'
+  },
+  docs: {
+    icon: 'i-heroicons-document-text-20-solid',
+    color: 'text-blue-500'
+  },
+  lock: {
+    icon: 'i-heroicons-lock-closed-20-solid',
+    color: 'text-gray dark:text-white'
+  },
+  default: {
+    icon: 'i-heroicons-question-mark-circle-20-solid',
+    color: 'text-green-500'
+  }
+}
+const links = [{
+  label: 'UDropdown and UPopover dropdown menu, dropdown will be obscured',
+  type: 'bug'
+}, {
+  label: 'Uncaught (in promise) ReferenceError: ref is not defined',
+  type: 'lock'
+}, {
+  label: 'Fully styled and customizable components for Nuxt.',
+  type: 'docs'
+}, {
+  label: 'Can I pass a tailwind color to UNotifications with `toast.add()` ?'
+}]
+</script>
+
+<template>
+  <UVerticalNavigation :links="links">
+    <template #icon="{ link }">
+      <UIcon v-if="link.type" :name="types[link.type].icon" :class="types[link.type].color" class="text-base" />
+      <UIcon v-else :name="types.default.icon" :class="types.default.color" class="text-base" />
+    </template>
+  </UVerticalNavigation>
+</template>