nix(refactor): Make with_tmp_db true checkedShellScript

This extends the interface of withTmpDb to allow loading different sets
of database fixtures via `postgrest-with-postgresql-xx --fixtures
<path>`.

test/fixtures/database.sql

@@ -1,3 +1,6 @@
+CREATE EXTENSION IF NOT EXISTS pgcrypto;
+ALTER DATABASE :DBNAME SET request.jwt.claim.id = '-1';
+
 set client_min_messages to warning;
 DROP SCHEMA IF EXISTS test, private, postgrest, jwt, public, تست, extensions, v1, v2 CASCADE;
 DROP TYPE IF EXISTS jwt_token CASCADE;