Allows users to execute ruby code that consumes classes
from app/models or any other portion of their app.

This is particularly helpful for creating smart columns for AR enums.
i.e.:

```ruby
 # app/models/account.rb
class Account < ApplicationRecord
  enum state: [:pending, :setup, :succeded, :failed]
end

 # config/blazer.yml
data_sources:
  main:
    smart_columns:
      account_state: <%= Account.states.to_h {|k,v| [v, k.titleize]}.to_json %>
```

Without this change, initialization fails with error "uninitialized
constant Account (NameError)".