EXCLUSIVE: Joy Nash, the YouTube star who this summer landed the lead role in AMC’s straight-to-series dark comedic drama Dietland from Marti Noxon, has signed with ICM Partners. The deal marks the latest step in Nash’s rise from a USC drama student whose video went viral to toplining a cable network series, and comes ahead of a November production start in New York on a 10-episode season. The Skydance TV-produced Dietland, adapted and directed by Noxon and based on Sarai…