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": "27481332-b477-48e2-9edd-2faffbdffd9f",
    "type": "retrospective_process_groups",
    "attributes": {
      "retrospective_process_id": "8a322aef-eba4-49ff-9431-572568109b60",
      "sub_status_id": "8e7baf79-4591-473d-9c39-70813b907d68",
      "position": 3,
      "updated_at": "2025-12-10T18:29:11.486-08:00",
      "created_at": "2025-12-10T18:29:11.486-08:00"
    },
    "relationships": {
      "retrospective_process_group_steps": {
        "data": []
      }
    }
  }
}