index receipts by the contract address

db/migrations/00030_create_receipt_cids_table.sql

@@ -3,6 +3,7 @@ CREATE TABLE public.receipt_cids (
   id                    SERIAL PRIMARY KEY,
   tx_id                 INTEGER NOT NULL REFERENCES transaction_cids (id) ON DELETE CASCADE DEFERRABLE INITIALLY DEFERRED,
   cid                   TEXT NOT NULL,
+  contract              VARCHAR(66),
   topic0s               VARCHAR(66)[]
 );