Actress Meg Ryan is giving Hamptons home buyers the opportunity to say, “I’ll have what she’s having,” as the “When Harry Met Sally” star discreetly listed her Bridgehampton farmhouse for $15.25 million last week, The Post has learned. The nearly 5,000-square-foot dwelling sits on 1.5-acres and takes a traditional approach, with brown wooden shingles, a covered porch and white pillars that recall a time when the Hamptons were a summer colony of clapboard houses and rolling hills. The residence