ecs-pino-format with convertReqRes wrong http field format

Hi,

I am using NestJS with [nestjs-pino](https://github.com/iamolegga/nestjs-pino) and I am trying to set up `ecsFormat({ convertReqRes: true })`. Logging of request and response works, but format is odd.
If this is meant for `nestjs-pino` i am sorry just let me know. Thank you

Versions I am using:
Node: 14.17.3
npm: 7.23.0
nestjs: latest setup
@elastic/ecs-pino-format: 1.3.0
nestjs-pino: 2.2.0
pino-http: 5.7.0

### Usage
```
@Module({
imports: [
LoggerModule.forRoot({
pinoHttp: { ...ecsFormat({ convertReqRes: true }) },
}),
],
})
export class AppModule {}
```

In this picture, you can see `ecsFormat` with` convertReqRes` set to `false` behaves as expected with `req` and `res` logged in their separate fields.

In this picture, convertReqRes was set to true. As you can see `response` field is in `HTTP`, but `req` is not and the log is missing `url` and `user_agent` fields (maybe others as well).

### Expected behavior
Correct format as shown in [elastic/pino-http-logging](https://www.elastic.co/guide/en/ecs-logging/nodejs/current/pino.html#pino-http-logging)

Thank you for your response, please let me know if this does not belong here.