[DOCUMENTATION] port settings for REST api in docker compose file.

On documentation page for RESTful API V2 it will be helpful if adjusted docker compose file with additional port property is mentioned in the area of [Enable RESTful Services](https://iotdb.apache.org/UserGuide/latest/API/RestServiceV2.html#enable-restful-services).

```
ports:
- "6667:6667"
- "18080:18080"
```

When users want to enable REST service, an additional port has to be added in the docker compose file.

Best regards
André

Open the RESTful API V2 documentation at the linked Enable RESTful Services section and review the Docker Compose example. Document the additional 18080:18080 port alongside the existing 6667:6667 mapping, then verify that the example explains the port required to enable the REST service.

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