title: Set filter before_action for ActiveAdmin controller
body: <p>I want to add <strong>before_action</strong> filter to ActiveAdmin controller.</p>
  
  <p>Could I do something like this:</p>
  
  <pre><code>before_action :set_product, only: [:show, :edit, :update, :destroy]
  
  private
  
  def set_product
    @product = Product.find_by_name(params[:name])
  end
  </code></pre>