Unable to use Peer auth

I want to have db-migrate authenticate by socket / peer auth, but this doesn't seem possible without hacking an env var.
```js

const dbMigrateConfig = {
default: 'local',
local: {
driver: 'pg',
database: 'mydatabase',
host: '/var/run/postgres',
native: true
}
};
```
'#ENOENT /var/run/postgres'

```
process.env['DBTEST'] = 'postgres:///${mydatabase}?host=/var/run/postgresql&native=true';
const dbMigrateConfig = {
default: 'local',
local: {
ENV: "DBTEST"
}
};
```

`success`.

Any chance the normal connection settings could allow connection via a socket?

---
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Start with the pg driver's normal connection-settings path and compare it with the ENV connection-string path shown in the issue. Verify how the database, host socket path, and native settings are passed, then confirm that the normal configuration can authenticate through a PostgreSQL peer socket without an environment variable.

Written by the indexing model from the issue text.