This will make a splash. Dozens of outdoor Big Apple pools are slated to open for the summer season this weekend — and Parks workers and maintenance crews are now racing to put the finishing touches. More than 50 massive outdoor pools across the five boroughs – including 13 Olympic-sized pools and 17 mini-pools meant for tots – will officially open Saturday at 11 a.m., a Parks rep confirmed to The Post. “Our maintenance staff has been working for weeks to prepare our pools,” the rep said, with