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": "6b7dc9e5-b8a3-486d-a198-16072cd56933",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "bb993582-9db6-465d-a2c0-ec2ef3125119",
      "retrospective_step_id": "89dbde59-4c51-4456-8337-cb219ee87b7c",
      "position": 1,
      "updated_at": "2025-07-23T05:32:15.089-07:00",
      "created_at": "2025-07-23T05:32:15.089-07:00"
    }
  }
}