Remove `ActiveRecord` based settings from generated `rails_helper`

Improve support for Rails apps which do not use `ActiveRecord`. This does not add settings in the generated `spec/rails_helper.rb` file which are specific to `ActiveRecord`. This allows new apps to run without modification, instead of raising errors.

**To Do**

- [x] Check for `ActiveRecord` in the `rails_helper.rb` template
- [x] Spec out changes to the template
- [x] Do not attempt to run migrations if the example app does not use `ActiveRecord`
- [x] Implement a 2nd set of smoke tests which do not use `ActiveRecord`
Thanks for the sanity check here. I actually didn't know what `self` was, so I tested and it seems `self` in this context is an instance of a `Rails::Generators::AppGenerator`. So this won't pollute anything.

I think it's worth adding a comment explaining this for my future self.