A major housing proposal could reshape part of Braintree. Town officials are reviewing plans for a 752-unit apartment complex on a 26-acre former industrial site off Plain Street in South Braintree. If approved, this would be one of the largest residential developments in the area — and the first major project under Braintree’s new MBTA Communities zoning rules. The proposal includes a mix of studio to three-bedroom apartments, affordable housing units, and over 1,100 parking spaces — all locate