docs: add CommandPalette async search example

docs/components/content/examples/CommandPaletteExampleAsync.vue

@@ -0,0 +1,21 @@
+<script setup>
+const groups = computed(() => {
+  return [{
+    key: 'users',
+    label: q => q && `Users matching “${q}”...`,
+    search: async (q) => {
+      if (!q) {
+        return []
+      }
+
+      const users = await $fetch(`https://jsonplaceholder.typicode.com/users`, { params: { q } })
+
+      return users.map(user => ({ id: user.id, label: user.name, suffix: user.email }))
+    }
+  }].filter(Boolean)
+})
+</script>
+
+<template>
+  <UCommandPalette :groups="groups" :autoselect="false" />
+</template>