feat(input): Allow to set "required" attribute

Fixes #163

docs/components/input/examples/InputRequiredExample.vue

@@ -0,0 +1,12 @@
+<template>
+    <div class="vp-raw">
+      <Input v-model='name' required placeholder="enter your first name" label="First name">
+      </Input>
+    </div>
+  </template>
+  <script lang="ts" setup>
+  import { ref } from 'vue'
+  import { Input } from '../../../../src/index'
+
+  const name = ref('')
+  </script>