While there are many attractions that draw visitors to Amsterdam nearly a quarter of this city’s more than four million foreign tourists a year will visit its coffee shops, where the sale of small quantities of cannabis is tolerated. But Amsterdam’s days as a destination for hazy holidays may be numbered. Prime Minister Mark Rutte’s right-wing coalition government is pushing to sharply restrict the operations of the coffee shops and to prohibit the sale of the drugs to nonresidents. If the measures survive a court challenge and the opposition of local officials, the first phase would begin May 1.