feat(SelectMenu): handle async search (#426)

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

docs/components/content/examples/SelectMenuExampleAsyncSearch.vue

@@ -0,0 +1,19 @@
+<script setup>
+const search = async (q) => {
+  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)
+}
+
+const selected = ref([])
+</script>
+
+<template>
+  <USelectMenu
+    v-model="selected"
+    :searchable="search"
+    placeholder="Search for a user..."
+    multiple
+    by="id"
+  />
+</template>