[aws]: Issue with AWS lambda logs in JSON format

### Integration Name

AWS [aws]

### Dataset Name

aws.lambda_logs

### Integration Version

3.16.0, 3.17.0

### Agent Version

9.0.3

### Agent Output Type

elasticsearch

### Elasticsearch Version

9.1.1

### OS Version and Architecture

Amazon Linux 2023

### Software/API Version

_No response_

### Error Message

No errors.

### Event Original

```json
{
// other document fields
...
"message": {
"timestamp":"2025-09-17T12:35:44.223Z",
"level":"ERROR",
"requestId":"438a7fca-64a7-4c80-ad62-9b43bb33fa86",
"message":{
"errorType":"Error",
"errorMessage":"Unsupported job \"undefined\"",
"stackTrace":["Error: Unsupported job \"undefined\""," at Runtime.handler (file:///var/task/index.mjs:68:16)"]
}
}
}
```

### What did you do?

I've configured AWS lambda (nodejs) to write logs in JSON format and configured elastic agent to use AWS lambda cloudwatch logs integration to collect these logs
Link to AWS nodejs lambda JSON logging docs: https://docs.aws.amazon.com/lambda/latest/dg/nodejs-logging.html

### What did you see?

Nothing was shown in kibana discovery. I was unable to find both lambda application logs (system logs was parsed properly) and documents with pipeline error

### What did you expect to see?

Same logs and in AWS CloudWatch in /aws/lambda/... log group. Application logs and lambda system runtime logs

### Anything else?

_No response_