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": "2687e70c-8abb-4913-a23f-d96d4c7f2819",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "0cf1ec58-7144-4ec7-b905-f5936fb542c8",
      "retrospective_step_id": "00f6da9c-ed22-4d27-a4df-dbf9175b87eb",
      "position": 1,
      "updated_at": "2025-09-03T02:24:53.943-07:00",
      "created_at": "2025-09-03T02:24:53.943-07:00"
    }
  }
}