It’s a patriotic display with pageantry three times over. The Big Apple will be celebrating a historic 250 years of military service in the US Tuesday – honoring a trio of trailblazing grand marshals at the 106th annual Veterans Day Parade. The commemoration, considered to be the nation’s largest Veterans Day tribute, will honor grand marshals from the Army, Navy and Marine Corps — including once-stranded NASA astronaut and retired Navy Capt. Sunita “Suni” Williams. “The 250th anniversary …