Grocery delivery app Instacart abruptly began charging Big Apple residents a new “regulatory response fee” this week after sweeping changes to the city’s delivery worker laws were enacted Monday, The Post has learned. “NYC regulatory response fees appear in the order summary,” the FAQ section of Instacart’s website now reads — a marked change from archived versions of the site just one month prior. An explanation of the fee reads that it “helps cover increased operating costs in NYC due to government regulations on delivery platforms.” A Post analysis of orders prior to Monday found no such fee tacked on....