feat(notifications): simplify how to position them

[atinux]

Resolves #185

Instead of using notifications.wrapper, add notifications.position and notifications.width for better control without having to copy the whole classes:

export default defineAppConfig({
  ui: {
    notifications: {
      // Show toasts at the top right of the screen
      position: 'top-0 right-0'
    }
  }
})