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": "c24407ae-ad0b-48ac-924a-432f50d6967b",
    "type": "retrospective_steps",
    "attributes": {
      "retrospective_process_id": "746ca917-5f35-48f2-82cc-95b99b96dc58",
      "title": "Step 1",
      "description": "Step 1 description",
      "incident_role_id": "cd587f24-a204-4b7d-9cb0-fc2095e16cd4",
      "due_after_days": 5,
      "position": 1,
      "skippable": false,
      "created_at": "2025-09-07T18:23:57.467-07:00",
      "updated_at": "2025-09-07T18:23:57.467-07:00"
    }
  }
}