The barrage of celebrity documentaries that have arrived in the wake of (and seemingly inspired by the success of) 2020’s “The Last Dance” tend to be exercises in image management. Unlike the dishier genre of celebrity memoir, these are scrapbooks for the screen. “Steve! (Martin) A Documentary in 2 Pieces” on Apple TV+ avoids some of those pitfalls better than most. Not entirely. Director Morgan Neville dutifully films Martin and collaborator Harry Bliss as they work on a 2022 memoir that tells the story of Martin’s career through cartoon anecdotes, and these moments serve no other purpose tha…