By Joey Roulette WASHINGTON (Reuters) – United Launch Alliance has pushed the debut launch of its new Vulcan rocket to early 2023 at the request of one of its customers, the company’s chief executive said, further delaying a benchmark mission crucial to the Boeing-Lockheed joint venture’s launch business. Vulcan, a roughly 200 foot-tall rocket in the final stages of development, will be the centerpiece to ULA’s launch business. It also will be a workhorse for U.S. Pentagon missions to space starting late next year as the rocket’s predecessor nears retirement over its use of Russian-made engine…