Two of the largest U.S. pharmacy chains, CVS Health and Walgreen Co., announced agreements in principle Wednesday to pay about $5 billion each to settle lawsuits nationwide over the toll of opioids, and a lawyer said Walmart is in discussions for a deal.Together, the developments amount to what could be the last round of huge settlements after years of litigation over the drug industry’s role in an overdose crisis that has been linked to more than 500,000 deaths in the U.S. over the past two decades.In the lawsuits …