Get all banners.

Example response

{
  "banners": [
    {
      "id": 7,
      "message": "**Reminder to everyone**: Maintenance is scheduled for *2337-12-27*.",
      "enabled": true,
      "variant": "info",
      "sticky": true,
      "icon": "build",
      "link": "dialog",
      "linkText": "Learn more",
      "dialogTitle": "Learn more about it here",
      "dialog": "# Information\n\nMaintenance is **scheduled**.\n\n## More details\n\nThis is an example dialog that supports Markdown.",
      "createdAt": "2023-12-27T13:37:00+01:00"
    }
  ]
}