docs: add notification examples (#20528)

Refs #20442

Adds the basic notification and notification with custom image examples from electron-api-demos into runnable Fiddle examples.

Gist links to Fiddles (same as code submitted in this PR):
Basic Notification: https://gist.github.com/102945f83f559e7944797175d8fd8af4
Notification with image: https://gist.github.com/2688bf4bfc27ce02f5d74224828eb928

Co-Authored-By: Erick Zhao <erick@hotmail.ca>

docs/fiddles/native-ui/notifications/basic-notification/renderer.js

@@ -0,0 +1,14 @@
+const notification = {
+  title: 'Basic Notification',
+  body: 'Short message part'
+}
+
+const notificationButton = document.getElementById('basic-noti')
+
+notificationButton.addEventListener('click', () => {
+  const myNotification = new window.Notification(notification.title, notification)
+
+  myNotification.onclick = () => {
+    console.log('Notification clicked')
+  }
+})