chore: DB defaults for managed platform, reduce required env vars

- db.js: DB_HOST default postgresqlk8s-master, DB_NAME default ipwhitelist, DB_USER default super
- server.js: fail-fast for DB_PASS in production (instead of IAM_API_URL)
- After this change: only DB_PASS is required for mock mode

src/db.js

@@ -2,10 +2,10 @@ const { Pool } = require('pg');
 require('dotenv').config();
 
 const pool = new Pool({
-  host: process.env.DB_HOST,
+  host: process.env.DB_HOST || 'postgresqlk8s-master',
   port: process.env.DB_PORT || 5432,
-  database: process.env.DB_NAME || 'postgres',
-  user: process.env.DB_USER,
+  database: process.env.DB_NAME || 'ipwhitelist',
+  user: process.env.DB_USER || 'super',
   password: process.env.DB_PASS,
   ssl: process.env.DB_SSLMODE === 'require' ? { rejectUnauthorized: false } : false,
   max: 10,