The title of the Jennifer Lopez documentary “Halftime” is not just a reference to the global superstar’s performance at halftime of the Super Bowl in 2020. It’s also meant as a nod to J. Lo’s 50th birthday just months before, and perhaps the midpoint of the actress, pop singer and mega-celebrity’s time on this planet. “Halftime” doesn’t quite give J. Lo the warts-and-all treatment; it’s a tightly managed portrait of Lopez’s life, career and unstoppable hustle, and there are no telling small moments that are going to threaten her carefully controlled image. Yet it’s a fascinating look at Lopez,…