BE: dont make bookings in the past

dont allow user to make bookings in the past.

either grey out dates on the calender that are in the past, or have a toast that says the date selected is in the past.

users should also not be able to make bookings in the past on a given day. eg. if it is Nov 8th, 3pm, they should not be able to book on Nov 8th BEFORE 3pm.