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": "0af02078-ae27-4fe9-8613-991c1f88e92a",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "4b80abab-e25e-461b-84f8-4f35998d2dbb",
      "retrospective_step_id": "eeaf7b3d-d3fe-4c19-b587-abb0de2b69c9",
      "position": 1,
      "updated_at": "2025-10-28T14:29:26.742-07:00",
      "created_at": "2025-10-28T14:29:26.742-07:00"
    }
  }
}