Feature Request - ISDB (Internet Services)

Policy responses can include ISDB references, therefore a GET request is needed to pull the ISDB.

Example from policy:
```
"internet-service": "enable",
"internet-service-id": [
{
  "q_origin_key": 393217,
  "id": 393217
}
],
"internet-service-custom": [],
```

The API endpoint is `cmdb/firewall/internet-service/`, I'm happy to do another PR?