Discord Inc. filed confidentially for an initial public offering, according to people familiar with the matter, adding to a rapidly growing pipeline of venture capital-backed tech listings.The San Francisco-based chat app company is working with Goldman Sachs Group Inc. and JPMorgan Chase & Co. on a listing, people familiar with the plans said in March. Discord, whose platform is popular with gamers and programmers, has more than 200 million monthly users, according to a statement in December....