Add Disable Private Mode Option

In Splash ,there is a option to disable the private mode (incognito mode), by default the private mode will be enabled in splash, this will lead to not able to crawl the sites that use localstorage. can you please add that an as option while generating the config files
Reference : [disable private mode in splash](https://splash.readthedocs.io/en/stable/faq.html#how-do-i-disable-private-mode)