Support env variables in DB config

Describe the feature

export default defineNitroConfig({
  database: {
    default: {
      connector: 'sqlite',
      options: { name: 'db' }
    },
    users: {
      connector: 'postgresql',
      url: 'postgresql://username:password@hostname:port/database_name'
    }
  }
})

Currently we define pgsql connection information in a configuration file.
I think it's dangerous to expose connection information in config files

Additional information

• Would you be willing to help implement this feature?

The issue does not name files, tests, or entry points. Start by locating Nitro's database configuration handling for the shown SQLite and PostgreSQL connectors; done means connection values can be supplied through environment variables without exposing them in the configuration file.