Creates a retrospective process group

curl --request POST \
  --url https://api.rootly.com/v1/retrospective_processes/{retrospective_process_id}/groups \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/vnd.api+json' \
  --data '{
  "data": {
    "type": "retrospective_process_groups",
    "attributes": {
      "sub_status_id": "<string>",
      "position": 123
    }
  }
}'

{
  "data": {
    "id": "2cf33698-0452-41dd-9f3a-cf1dc482df89",
    "type": "retrospective_process_groups",
    "attributes": {
      "retrospective_process_id": "c2616166-ac6c-4af7-9c24-abdeeab5bf6f",
      "sub_status_id": "b30095a6-4b78-4411-b253-3d57e9d4fa13",
      "position": 3,
      "updated_at": "2025-11-20T08:47:02.763-08:00",
      "created_at": "2025-11-20T08:47:02.763-08:00"
    },
    "relationships": {
      "retrospective_process_group_steps": {
        "data": []
      }
    }
  }
}