Brian Steinberg Senior TV EditorDiscovery revealed the big challenge behind getting involved in the media industry’s streaming wars: A new broadband hub can bring in millions of new customers — but it also requires millions of dollars in investment.The New York owner of Food Network, HGTV, TLC and its flagship Discovery cable outlet said Wednesday that its first-quarter profit slumped after it ramped up spending for content and marketing related to Discovery Plus, the streaming-video outlet it