API - RSSI and relay device added to latest samples endpoints

✨ Improvements

Battery status (percentage), rssi (signal strength) and relay device type have been added the following
endpoints:

/devices/{serialNumber}/latest-samples
/locations/{locationId}/latest-samples

rssi is only visible for devices which are connected to a hub. relayDeviceType will be "hub" when
the device is connected to a hub and "app" when an app is used to sync data from the device.

Example response:

{
  "data": {
    "co2": 491.0,
    "humidity": 16.0,
    "light": 45,
    "pressure": 1027.8,
    "radonShortTermAvg": 39.0,
    "temp": 22.2,
    "time": 1616143854,
    "virusRisk": 7.0,
    "voc": 54.0,
    "rssi": -45,
    "battery": 83,
    "relayDeviceType": "hub"
  }
}