Add an asset to an asset group

Example request

{
  "default_values": {
    "fuel_type": {
      "value": "Eastern",
      "unit": "",
      "measurement_type": "measurement_type",
      "measurement_quantity": "dimensionless_coefficient"
    },
    "volume": {
      "value": 5,
      "unit": "e3m3",
      "measurement_type": "measurement_type",
      "measurement_quantity": "volume"
    },
    "rvp": null
  }
}