docs(carousel): add thumbnails example (#3740)

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

docs/app/components/content/examples/carousel/CarouselThumbnailsExample.vue

@@ -0,0 +1,54 @@
+<script setup lang="ts">
+const items = [
+  'https://picsum.photos/640/640?random=1',
+  'https://picsum.photos/640/640?random=2',
+  'https://picsum.photos/640/640?random=3',
+  'https://picsum.photos/640/640?random=4',
+  'https://picsum.photos/640/640?random=5',
+  'https://picsum.photos/640/640?random=6'
+]
+
+const carousel = useTemplateRef('carousel')
+const activeIndex = ref(0)
+
+function onClickPrev() {
+  activeIndex.value--
+}
+function onClickNext() {
+  activeIndex.value++
+}
+
+function onSelect(index: number) {
+  activeIndex.value = index
+
+  carousel.value?.emblaApi?.scrollTo(index)
+}
+</script>
+
+<template>
+  <div class="flex-1 w-full">
+    <UCarousel
+      ref="carousel"
+      v-slot="{ item }"
+      arrows
+      :items="items"
+      :prev="{ onClick: onClickPrev }"
+      :next="{ onClick: onClickNext }"
+      class="w-full max-w-xs mx-auto"
+    >
+      <img :src="item" width="320" height="320" class="rounded-lg">
+    </UCarousel>
+
+    <div class="flex gap-1 justify-between pt-4 max-w-xs mx-auto">
+      <div
+        v-for="(item, index) in items"
+        :key="index"
+        class="size-11 opacity-25 hover:opacity-100 transition-opacity"
+        :class="{ 'opacity-100': activeIndex === index }"
+        @click="onSelect(index)"
+      >
+        <img :src="item" width="44" height="44" class="rounded-lg">
+      </div>
+    </div>
+  </div>
+</template>