Before there was a Malia Obama or a Chelsea Clinton, there was Steve Ford. The third son of President Gerald Ford and Betty Ford, Steve Ford was 18 when his father took office following the resignation of President Richard Nixon in 1974. He spent his post-White House life far from politics — he was an actor for nearly three decades, racking up small roles on movies and TV shows from “When Harry Met Sally” to “Baywatch,” and is best known for the near decade he spent on the cast of the CBS soap, “The Young and the Restless.” Ford stepped away from the cameras eight years ago to devote more time to the foundation that supports his father’s presidential library and museum, mostly quiet, behind-the-scenes work, though now he’s promoting a new documentary about his father’s life and legacy: on May 27, the National Geographic Channel will debut “Gerald R.