Creates a retrospective step

curl --request POST \
  --url https://api.rootly.com/v1/retrospective_processes/{retrospective_process_id}/retrospective_steps \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/vnd.api+json' \
  --data '{
  "data": {
    "type": "retrospective_steps",
    "attributes": {
      "title": "<string>",
      "description": "<string>",
      "due_after_days": 123,
      "incident_role_id": "<string>",
      "position": 123,
      "skippable": true
    }
  }
}'

{
  "data": {
    "id": "6db645b1-b6c1-46d3-9816-15c72d95a0cf",
    "type": "retrospective_steps",
    "attributes": {
      "retrospective_process_id": "2337a5d8-3db8-4b60-94bc-efb81e9855b7",
      "title": "Step 1",
      "description": "Step 1 description",
      "incident_role_id": "a3e9708e-bb4c-483a-ac63-44beaf4b7f6f",
      "due_after_days": 5,
      "position": 1,
      "skippable": false,
      "created_at": "2025-05-29T17:47:41.236-07:00",
      "updated_at": "2025-05-29T17:47:41.236-07:00"
    }
  }
}