Singapore’s contact-tracing phone app, TraceTogether, will remain voluntary for “as long as possible”, Foreign Minister Vivian Balakrishnan said.“It is a hybrid system based on public support, keeping public trust, and maintaining privacy,” Balakrishnan said.“I think it is very important to have those features, because otherwise contact tracing will not work,” the minister said in an interview with Sky News Australia.About 1.5 million residents have downloaded the app, or between 20 and 25 per…