The joint streaming venture that will combine some of the most valuable assets in sports media will be called Venu Sports, the service’s chief executive announced on Thursday. In February, Warner Bros. Discovery, Fox Corp. and Disney’s ESPN announced they were teaming up to offer a new sports streaming service that includes all their sports programming from National Hockey League games to next year’s Super Bowl. Venu Sports, which is set to make its debut in the fall, is another example of how media giants are trying to establish themselves in the world of streaming as millions of Americans cut the cord every year and large technology companies have entered the marketplace for valuable sports rights.