debezium의 exactly once, at least once

https://debezium.io/docs/connectors/mysql/#when-things-go-wrong

<장애 요약>
- exactly once이지만 장애시에는 at least once가 될 수 있다. (우리 요구사항을 충족한다)
- 여러 컴포넌트 장애가 있어도 다 처리한다.