Response /ivp/ensemble/power

Response from enphase Envoy vD8.2.4382

```
{
    "devices:": [
        {
            "serial_num": "xxxxxxxxxxxx",
            "real_power_mw": -1263000,
            "apparent_power_mva": -1263000,
            "soc": 88
        }
    ]
}
```

These endpoint shows the state of each battery: 

- Current State of Charge
- Charge/Discharge rates