Add Postgres Create trigger support

We have a trigger that updates the field time

```sql
CREATE OR REPLACE FUNCTION updated_at() RETURNS trigger AS $$
BEGIN
IF (
NEW IS DISTINCT FROM OLD AND
NEW.updated_at IS NOT DISTINCT FROM OLD.updated_at
) THEN
NEW.updated_at := current_timestamp;
END IF;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
```

The issue provides a PostgreSQL PL/pgSQL example but names no repository files, entry points, or tests. Locate the PostgreSQL CREATE TRIGGER parsing entry point and existing parser tests; done means the shown trigger-related SQL is accepted with regression coverage.

Written by the indexing model from the issue text.