Employer-employee relations — Whistleblowers — Retaliation — Trial court erred in granting summary judgment in favor of plaintiff’s former employer based on “manager rule” where genuine issue of material fact existed as to whether plaintiff stepped outside his role as manager and engaged in protected oppositional conduct, whether plaintiff had good faith, objectively reasonable belief that former employer engaged in unlawful activity, and whether plaintiff’s objections were “but for” cause of non-renewal of employment agreement