Can we add GIFs as bot replies on WhatsApp?

Yes, you can paste the following JSON in the Raw Text/JSON chat element.

{
  "type": "CAROUSEL",
  "data": {
    "image_aspect_ratio": "1",
    "width": "BIG",
    "items": [
      {
        "thumbnail": {
          "image": "<REPLACE WITH LINK TO GIF>"
        },
        "title": "",
        "actionables": []
      }
    ]
  },
  "isNew": false
}