A trip out to Rockville is no minor undertaking for a committed city dweller, but the Jewish Community Center of Greater Washington hosts a concert series that offers regular enticement. For the Sunday evening recital by Bejun Mehta (his first ever in the Washington area), rain did not prevent an impressive crowd from filling the center’s small auditorium. The celebrated American countertenor has been in town this month, for the Washington Concert Opera’s performance of…