Good morning. You're reading the Up First newsletter. Subscribe here to get it delivered to your inbox, and listen to the Up First podcast for all the news you need to start your day. Today's top stories World leaders convene this week in New York for the United Nations General Assembly. It will be U.N. Secretary-General António Guterres' last General Assembly before his term ends in December. He will open the event on Tuesday morning, followed by Brazilian President Luiz Inácio Lula da Silva, and then President Trump. Here's what NPR will be watching throughout the high-level event, which runs through Sept. 28. U.N….