Sebastian Siemiatkowski, CEO of Klarna, speaking at a fintech event in London on Monday, April 4, 2022.Chris Ratcliffe | Bloomberg via Getty ImagesSwedish fintech firm Klarna will be the exclusive provider of buy now, pay later loans for Walmart, taking a coveted partnership away from rival Affirm, CNBC has learned.Klarna, which just disclosed its intention to go public in the U.S., will provide loans to Walmart customers in stores and online through the retailer's majority-owned fintech startup...