Lack of Cognito SMS Lambda Trigger

I couldn't seem to find a class available for the SMS Lambda Trigger, see https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-lambda-custom-sms-sender.html

This seems relatively easy to add, there are 2 extra fields here:
- `code`
- `type` (this is static for every event sent to the SMS Lambda trigger)

It doesn't require a response but a user of this can just return the empty event or no event, just to keep in line with other lambda events and just in case there is an update in the future, it will easier to move towards this new update.

首先，將現有的 Cognito Lambda trigger event classes 與 issue 中連結的 AWS custom SMS sender 文件進行比較。識別代表此 trigger 的類別，並驗證新的 event definition 暴露了 code 和靜態型別，同時與相鄰的 trigger classes 保持一致。當 Java consumers 可以使用 SMS trigger event 而不需要 response 時，即表示完成。

由索引模型根據 Issue 內容生成。