A developer has filed plans for a five-story, 38-unit apartment building at 36 Parker Hill Ave., at Hillside Street on Mission Hill. The proposal, by Jason Savage’s Savage Properties of Allston, calls for the units to be split between studios and two-bedroom apartments. Its filing with the Boston Planning Department does not say how many of the units will be affordable, but if it complies with new affordable-units that came into effect Oct. 1, six or seven would have to be provided.