A big change is coming to the agency tasked with developing a bullet-train system to link Northern and Southern California through the San Joaquin Valley with the coming resignation of its top executive. Brian Kelly, who has led the California High-Speed Rail Authority as its CEO since early 2018, announced Thursday that he will step down from the post. Kelly submitted his formal letter of resignation to the authority’s board chairperson, Fresno developer Tom Richards. Kelly told The Fresno Bee that he plans to stay in the role, perhaps for several months or more, as the agency begins its sear…