chore(storybook): add CSF3 default render example story

examples/vue-kitchen-sink/src/stories/Button.vue

@@ -6,7 +6,9 @@
     @click="onClick"
     @dblclick="onDoubleClick"
   >
-    <slot />!
+    <slot>
+      {{label}}!
+    </slot>
   </button>
 </template>
 
@@ -23,6 +25,9 @@
       color: {
         type: String,
         default: '#42b983'
+      },
+      label: {
+        type: String
       }
     },
 

examples/vue-kitchen-sink/src/stories/components/button.stories.js

@@ -27,3 +27,11 @@ Square.args = {
   color: '#00f',
   label: 'A Button with square edges',
 };
+
+export const WithDefaultRender = {
+  args: {
+    rounded: true,
+    color: '#fba',
+    label: 'Button with default render',
+  },
+};