Nickelodeon went through a golden period in the late ’90s and early ’00s, churning out popular shows like “All That” and “iCarly” with the help of its hit-making producer Dan Schneider.But a new documentary series featuring several former child stars is bringing forth allegations of a toxic work environment on some of Schneider’s former popular Nick shows. “Quiet on Set: The Dark Side of Kids TV,” which will air on Investigation Discovery on March 17 and 18, comes two years after Business Insider interviewed several people who worked directly with Schneider. The report…