For all driver set property

driver.additional.capabilities={<capabilityname1>=<value1>,<capabilityname2>=<value2>}

For specific driver set property

<driver>.additional.capabilities={<capabilityname1>=<value1>,<capabilityname2>=<value2>}

Example:

chrome.additional.capabilities={"chromeOptions":{"mobileEmulation":{"deviceName":"Apple iPhone 5"}}}