title: simple_form collection labels
body: <p>I want to use labels for collection items (for example, their translations).</p>
  
  <pre><code>= simple_form_for(@client) do |f|
    = f.error_notification
      .form-inputs
        = f.input :name, label: t('client.name')
        = f.input :level, collection: ['a', 'b', 'c'],
          label_method: ????
          label: t('client.level')
      .form-actions
        = f.button :submit, value: t('client.submit')
  </code></pre>
  
  <p>I am trying to figure out, what to use for <code>label_method</code> above.
  I would like to have label_method to map to translations as in <code>map {|s| t("client.#{s}")}</code>.</p>