Adding flag in website responder to get this information at the very begging of web app lifecycle.
I did some research and there is no one good method for detecting it is mobile browser. I choose solution which I think is most likely to work, but it'll be good to revisit this in the future [ENG-3407](https://linear.app/comm/issue/ENG-3407/revisit-method-for-detecting-mobile-browser).