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": "1de4dd3a-a26b-4de9-9ab5-50310f697df4",
    "type": "retrospective_steps",
    "attributes": {
      "retrospective_process_id": "df693307-fb2f-4006-af1c-1bb142fd2e2f",
      "title": "Step 1",
      "description": "Step 1 description",
      "incident_role_id": "44b6bf0c-d80c-46bf-a1ff-a360a285a331",
      "due_after_days": 5,
      "position": 1,
      "skippable": false,
      "created_at": "2026-01-21T13:47:06.362-08:00",
      "updated_at": "2026-01-21T13:47:06.362-08:00"
    }
  }
}