Amazon announced on Thursday that it narrowed its list of potential cities for its second headquarters to 20. The Seattle-based tech giant said it reviewed 238 proposals from across the U.S., Canada, and Mexico to host its so-called HQ2, the company's second headquarters in North America. Today, Amazon announced it has chosen the following 20 metropolitan areas to move to the next phase of the process: Amazon said it expects to invest $5 billion and hire up to 50,000 workers for the campus.…