Joshua Kushner’s sudden rise to co-ownership of the most storied team in professional basketball might seem like it came out of the blue — but it’s been a long time coming.A scion of the wealthy Kushner family whose older brother, Jared, is married to President Trump’s daughter, and whose father, Charles, is the U.S. ambassador to France, has successfully staked out his own lucrative business career. He’s worth an estimated $5.2 billion, according to Forbes.Along the way, the New York-based entrepreneur and venture capitalist has exhibited a deep interest in sports investments. This summer, there were reports that Kushner and...