Creates a retrospective process group step

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

{
  "data": {
    "id": "839af62f-2ccb-411d-bc01-0cac53d4da6e",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "643307da-bd10-4701-a339-dbd7ba96be31",
      "retrospective_step_id": "a1e8ccaa-135b-4ede-b3f1-8be0f5e60a9d",
      "position": 1,
      "updated_at": "2026-02-07T16:50:12.609-08:00",
      "created_at": "2026-02-07T16:50:12.609-08:00"
    }
  }
}