Trust the user when establishes a counter cache column

We have problems running

```sh
bundle exec rake db:create
```

That raise due to that code tries to get a connection to the database when even not exists yet.

Adding any extra code will add a lot complexity that IMHO is not needed. If the user provides a column to use as counter_cache column I think we should use that column directly.

In our case we have `Devise.invited_by_counter_cache` with the default value `nil` and still trying to ask for the counter_cache column in the table