feat(table): add slot for empty state (#260)

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

docs/components/content/examples/TableExampleEmptySlot.vue

@@ -0,0 +1,30 @@
+<script setup>
+const columns = [{
+  key: 'name',
+  label: 'Name'
+}, {
+  key: 'title',
+  label: 'Title'
+}, {
+  key: 'email',
+  label: 'Email'
+}, {
+  key: 'role',
+  label: 'Role'
+}, {
+  key: 'actions'
+}]
+
+const people = []
+</script>
+
+<template>
+  <UTable :rows="people" :columns="columns">
+    <template #empty-state>
+      <div class="flex flex-col items-center justify-center py-6 gap-3">
+        <span class="italic text-sm">No one here!</span>
+        <UButton label="Add people" />
+      </div>
+    </template>
+  </UTable>
+</template>