By the early 1900s, Greenwich,Connecticut, with its proximity to New York City, good beaches, nice summer weather and a deep harbor for yachts, had attracted some of America’s richest people who built massive mansions for full-time living or smaller “summer cottages,” that were still quite large, for seasonal stays.   One of the prettiest of Greenwich’s great estates was Sunridge Farm built in 1900 for John B. Pierce, the founder of American Standard Company. Sunridge Farm has just come on the market priced at $9.208 million.