"[E]mployers with between 50 and 499 employees that are not healthcare providers must provide two full weeks of paid sick leave ... for employees who need to take leave for any reason for which employees may take leave under the [FFCRA].... Employers can only require certification of the need for leave if the employee uses three or more consecutive working days of paid leave, and cannot require that the certification be provided sooner than one week after the employee returns to work."