“Rust” cinematographer Halyna Hutchins, 42, who was shot and killed at the accidental hand of Alec Baldwin on the set of “Rust,” will be the subject of an upcoming documentary. The project has already been green-lit by Halyna’s widower, Matt Hutchins, according to Variety. Emmy-nominated director Rachel Mason (“Circus of Books”) is set to helm, while Julee Metz will serve …