feat(SelectMenu): add empty slot when no options

Resolves #1089

docs/components/content/examples/SelectMenuExampleEmptySlot.vue

@@ -0,0 +1,13 @@
+<script setup>
+const people = []
+
+const selected = ref()
+</script>
+
+<template>
+  <USelectMenu v-model="selected" :options="people">
+    <template #empty>
+      No people
+    </template>
+  </USelectMenu>
+</template>

docs/content/3.forms/4.select-menu.md

@@ -232,6 +232,18 @@ Use the `#option-create` slot to customize the content displayed when the `creat
 An example is available in the [Create option](#create-option) section.
 ::
 
+### `empty`
+
+Use the `#empty` slot to customize the content displayed when there is no options. Defaults to `No options.`.
+
+::component-example
+---
+component: 'select-menu-example-empty-slot'
+componentProps:
+  class: 'w-full lg:w-48'
+---
+::
+
 ## Props
 
 :component-props