title: Created woocommerce product attribute programmatically and added terms to them but terms are not showing in Product->Attributes
body: <p>I have created woo-commerce product attributes programmatically by the following code:</p>
  
  <pre><code>$data = array(
      'name'   =&gt; 'My attribute',
      'slug'    =&gt; wc_sanitize_taxonomy_name(wp_unslash('My attribute')),
      'type'    =&gt; 'select',
      'order_by' =&gt; 'menu_order',
      'has_archives'  =&gt; 1
    );        
   wc_create_attribute( $data );
  </code></pre>
  
  <p>and this code adds attributes successfully and are visible to the list of woo-commerce in Products->Attributes, but after that, I tried adding  some <code>terms</code> to them which are not affected to the attribute list by using following code:</p>
  
  <pre><code>wp_insert_term( 'term_1' ,'pa_'.$data['slug']);
  </code></pre>
  
  <p>also, I confirm that when I dump the result of <code>var_dump(get_term_by('name','term_1','pa_'.$data['slug']))</code> I get result with term id,name,slug,term_taxonomy_id etc., but the problem it these terms are not visible on the woocommerce product attributes and so does on product editing page.</p>