If you take a stroll down Boylston Street in the Back Bay, you’ll see new bank branches spreading like kudzu. Admirals Bank is planning to open its first Boston banking center on the street in two weeks. Capital One Bank is taking over the prominent storefront once used by Anthropologie, the women’s clothing store, as part of its plans to expand to Massachusetts. And Bank of America, which already has three locations on Boylston, is in negotiations to fill the space now occupied by jeweler Shreve, Crump & Low. Boylston Street has become Ground Zero as banks battle for customers.