support sql_translator_args

To generate proper SQL for ENUM in PostgreSQL, I need to specify the postgres_version for the SQL::Translator producer (see https://metacpan.org/source/FREW/SQL-Translator-0.11016/lib/SQL/Translator/Producer/PostgreSQL.pm#L473)

With this patch, I can now say:

```
DBIx::Class::Migration::Script->run_with_options(
    schema => ...,
    databases => ['PostgreSQL'],
    sql_translator_args => { producer_args => { postgres_version => '9.1' } }
);
```

... in my deployment script. Does this look feasible, or are there any other more preferred ways to achieve this? I could use DBIx::Class::Migration directly, but I'd really like to use the already existing Script.pm.