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": "89430bd4-5d02-4b85-a8dd-7d7b52d37258",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "9541222a-2fbd-44b0-b93c-9fe11ca28504",
      "retrospective_step_id": "d743fa1b-6c9a-4372-9fa4-c99d04f4f7b6",
      "position": 1,
      "updated_at": "2026-02-10T15:56:46.202-08:00",
      "created_at": "2026-02-10T15:56:46.202-08:00"
    }
  }
}