Missing or unclear type definitions in "Integration of Amazon DocumentDB with AWS Lambda" typescript snippet

The code snippet in `integration-docdb-to-lambda/example.ts` includes the following two types:
```typescript
import { DocumentDBEventRecord, DocumentDBEventSubscriptionContext } from 'aws-lambda';
```

However, it is unclear what the source of these types is. The name "aws-lambda" suggests they might be part of the @types/aws-lambda package, but that package does not define these types. Additionally, I was unable to find any other package named "aws-lambda" that provides them.

It would be helpful to clarify the origin of these types, or define them directly within the snippet.