function mergeWithExistingDevice(tasmotaDevice) {
  const existing = this.gladys.stateManager.get('deviceByExternalId', tasmotaDevice.external_id);
  return mergeDevices(tasmotaDevice, existing);
}
@description Get all discovered devices, and if device already created, the Gladys device.
@param {object} tasmotaDevice - Discovered device.
@returns {object} Device merged with Gladys existing one.
@example
mergeWithExistingDevice(discorveredDevice)