feat(SelectMenu): add value-attribute prop (#429)

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

docs/components/content/examples/SelectMenuExampleObjectsValueAttribute.vue

@@ -0,0 +1,33 @@
+<script setup>
+const people = [{
+  id: 1,
+  name: 'Wade Cooper'
+}, {
+  id: 2,
+  name: 'Arlene Mccoy'
+}, {
+  id: 3,
+  name: 'Devon Webb'
+}, {
+  id: 4,
+  name: 'Tom Cook'
+}]
+
+const selected = ref(people[0].id)
+
+const current = computed(() => people.find(person => person.id === selected.value))
+</script>
+
+<template>
+  <USelectMenu
+    v-model="selected"
+    :options="people"
+    placeholder="Select people"
+    value-attribute="id"
+    option-attribute="name"
+  >
+    <template #label>
+      {{ current.name }}
+    </template>
+  </USelectMenu>
+</template>