Query assistant for public_contributions

Schema that will be passed to the model

CREATE TABLE public_contributions ("canon_id", "donor_name", "employer", "occupation", "is_organization", "city", "state", "zip", "amount", "date", "is_inkind", "designated_election_phase", "campaign_id", "reporting_period", "party", "election_cycle_year", "candidate_name", "office_name");
CREATE INDEX idx_pc_pair ON public_contributions(canon_id, campaign_id);
CREATE INDEX idx_pc_campaign ON public_contributions(campaign_id)