title: Laravel Nova - Load dropdown field based on relationship with of another dropdown
body: <p>I have this resource called <code>Distributor</code></p>
  
  <pre><code>  ID::make()-&gt;sortable(),
              Text::make('Name')
                  -&gt;creationRules('required'),
              BelongsTo::make('Region')
                  -&gt;creationRules('required')
                  -&gt;searchable(),
              BelongsTo::make('Country')
                  -&gt;creationRules('required')
                  -&gt;searchable(),
  </code></pre>
  
  <p>Everything is on place till now. But the <code>Country</code> model should depend on <code>Region</code>model, so when I select a region I want to display options with countries related to that Region.</p>
  
  <p>Region and Country are already related in their models based on <code>belongsToMany</code> relationships.</p>
  
  <p>Is there a way to do this fields work together?</p>