Add tip warning for OLO/and custom tip on POS

Something that is really needed is a tip warning... I'm all for our employees getting tipped generously but accidents where customer's accidentally leaves $1000 tips (which we've seen more than once) can be avoided by putting up a message if a tip exceeds a certain threshold. I think it would be good to have a setting in the back office that lets your clients pick their threshold based on percentage/amount.