add different error format for 23505 error on postgres

Would you guys like me to submit a failing test for this? Do you guys test this kind of thing?

Also, I tried to find somewhere on postgres where it mapped error codes into error messages but I didn't find it. Any idea on if this exists out there? There might be even more error formats for code 23505 or other codes...
Yea it would output this:

```
SequelizeUniqueConstraintError: Could not further parse error message.
```