feat: add gradient(monochrome, duotone), outline colored button. prefix and suffix slots button

docs/guide/button/examples/ButtonGradientDuotoneExample.vue

@@ -0,0 +1,14 @@
+<template>
+  <div class="inline-flex align-center gap-2 flex-wrap">
+    <Button gradient="purple-blue">Purple to blue</Button>
+    <Button gradient="cyan-blue">Cyan to blue</Button>
+    <Button gradient="green-blue">Green to blue</Button>
+    <Button gradient="purple-pink">Purple to pink</Button>
+    <Button gradient="pink-orange">Pink to orange</Button>
+    <Button gradient="teal-lime">Teal to lime</Button>
+    <Button gradient="red-yellow">Red to yellow</Button>
+  </div>
+</template>
+<script setup>
+import { Button } from '../../../../src/index'
+</script>