PARIS/MOSCOW, Aug 25 (Reuters) - Pavel Durov, the Russian-born billionaire founder and owner of the Telegram messaging app, was arrested at Le Bourget airport outside Paris shortly after landing on a private jet late on Saturday and placed in custody, three sources told Reuters. The arrest of the 39-year-old technology billionaire prompted on Sunday a warning from Moscow to Paris that he should be accorded his rights and criticism from X owner Elon Musk who said that free speech in Europe was under attack. There was no official confirmation from France of the arrest, but two French police sources and...