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": "96d3472c-c0fc-402c-9e46-86c6da1d92e0",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "11805303-9105-4d3f-9d54-157fd61ce571",
      "retrospective_step_id": "f9a75d12-5908-4416-b0cb-ef3553b353f2",
      "position": 1,
      "updated_at": "2025-10-08T13:09:36.721-07:00",
      "created_at": "2025-10-08T13:09:36.721-07:00"
    }
  }
}