By Hannah Lang and Pete Schroeder April 10 (Reuters) - Crypto giant Kraken's landmark Federal Reserve master account comes with restrictions aimed at mitigating risks, but it - and others likely to follow in its wake - could still create vulnerabilities for the U.S. financial system. Founded in 2011, Wyoming-based Kraken is one of the world's largest crypto exchanges, with both retail and institutional clients. Last month, it became the first-ever ‌crypto company to win a Fed master account. The Kansas C ...