Allow to set wrapper mappings when SimpleForm.setup

[snkanta]

Like #1632, I want to specify different wrapper mappings for each wrapper of form.
So, I would like to be able to specify the wrapper mappings for the wrapper of form when SimpleForm.setup.

# config/initializers/simple_form.rb
SimpleForm.setup do |config|
  # ...

  horizontal_forms_mapping = {
    boolean:       :horizontal_boolean,
    check_boxes:   :horizontal_collection,
    date:          :horizontal_multi_select,
    datetime:      :horizontal_multi_select,
    file:          :horizontal_file,
    radio_buttons: :horizontal_collection,
    range:         :horizontal_range,
    time:          :horizontal_multi_select
  }

  # horizontal form wrapper
  config.wrappers :horizontal_form, tag: 'div', class: 'mb-4', wrapper_mappings: horizontal_forms_mapping do |b|
    b.use :html5
    b.use :placeholder

    # ...

  end

  # ...
end