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": "9fff8658-4cb8-4563-a524-2597d1816da9",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "9fd3dd7e-f19b-4535-abe1-f9a9cd20da11",
      "retrospective_step_id": "43107230-516d-4040-abfe-96850f1cf65f",
      "position": 1,
      "updated_at": "2025-10-29T14:47:56.509-07:00",
      "created_at": "2025-10-29T14:47:56.509-07:00"
    }
  }
}