title: Custom button in ActiveAdmin
body: <p>On ActiveAdmin, I have a form like this:
  Note that "My thingy" is not on the DB, but calculated with the data from an API.
  <a href="https://i.stack.imgur.com/xySNT.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xySNT.png" alt="enter image description here"></a></p>
  
  <p>I want to add a filter for this field. What I'd like is to send this <code>abc</code> text as a parameter to the same edit action in which I am.</p>
  
  <p><a href="https://i.stack.imgur.com/Fz4hz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Fz4hz.png" alt="enter image description here"></a></p>
  
  <p>My form looks like this:</p>
  
  <pre><code>form do |f|
    f.inputs "Details" do
      f.input :my_thingy,
        label: 'My thingy',
        as: :select,
        collection: my_thingys,
      f.input :my_thingy_filter, label: "Filter My thingy by..."
      f.button :filter
    end
    f.actions
  end
  </code></pre>
  
  <p>What I'd like is for this button to redirect to the same page, with the value of <code>my_thingy_filter</code> as a parameter.</p>
  
  <p>How can I do that?</p>