FRANKFURT, June 23 : The European Central Bank secured key parliamentary backing on Tuesday for the launch of a digital euro, an electronic means of payments aimed at making the euro zone less reliant on U.S. credit cards at a time of fraying transatlantic relationships. The digital euro, essentially an electronic wallet guaranteed by the central bank but marketed by banks or fintech companies, will allow all euro zone residents to make payments online and in person. Six years in the making,