Add light sync transactions table

- Foreign key to header instead of block
- Can use same Transaction struct for both

pkg/contract_watcher/shared/helpers/test_helpers/database.go

@@ -240,6 +240,9 @@ func TearDown(db *postgres.DB) {
 	_, err = tx.Exec(`DELETE FROM full_sync_transactions`)
 	Expect(err).NotTo(HaveOccurred())
 
+	_, err = tx.Exec("DELETE FROM light_sync_transactions")
+	Expect(err).NotTo(HaveOccurred())
+
 	_, err = tx.Exec(`DELETE FROM receipts`)
 	Expect(err).NotTo(HaveOccurred())