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": "64ead047-e83b-49b5-8745-b3651b08c732",
    "type": "retrospective_process_group_steps",
    "attributes": {
      "retrospective_process_group_id": "a0613d9b-cdea-4d74-8d91-5ca9f3dd9815",
      "retrospective_step_id": "19625f17-c67e-4495-b2d4-476edc5b5612",
      "position": 1,
      "updated_at": "2025-08-12T10:50:37.013-07:00",
      "created_at": "2025-08-12T10:50:37.013-07:00"
    }
  }
}