CEDAR RAPIDS — The intersection of Eighth Avenue SE and Fifth Street SE in Cedar Rapids is a heavily trafficked one. It’s a tiny pocket of Cedar Rapids that falls at the crossroads of three areas, tucked as it is between the city’s downtown core and the MedQuarter medical district, and just north of the NewBo District. Yet the area is picking up with dining activity, both new and old. Boston Fish Market, at 804 Fifth St.