By Inna Varenytsia DONETSK REGION, Ukraine (Reuters) – A Ukrainian soldier near the front line looks into video goggles and clutches a control set in both hands as he guides a drone during the war against Russia. The soldier, who goes by the call sign “Sam”, looks up and complains: “There’s no video.” Unmanned aerial vehicles (UAVs), or drones, have become vital for Ukraine’s military since Russia’s full-scale invasion in February 2022. Hundreds can buzz over Russian positions in eastern and southern Ukraine at any one time. But many of them are hastily and cheaply assembled by volunteers, and…