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"}}}