JPMorgan Chase CEO Jamie Dimon has been communicating with Donald Trump in recent months through secret back channels, helping the president-elect hammer out a policy agenda before and since his decisive White House victory, The Post has learned. The 68-year-old Wall Street titan — who, like 78-year-old Trump, grew up in Queens in New York City — has acted as “a sounding board” for the incoming commander-in-chief’s economic manifesto, four sources close to Trump’s transition team *** The quietly cozy relationship between Trump and Dimon has flourished despite the banker’s cryptic and tight-lipped tendencies when it comes to politics. Trump...