title: Add image upload custom field at dokan template new-product.php
body: <p>I am using dokan plugin for a multivendor website, I want to add image upload custom field in the template
   new-product.php, I used CMB2 plugin to create image upload custom field with WooCommerce like this </p>
  
  <pre><code>          function themebox_metaboxes() {
  
          // Start with an underscore to hide fields from custom fields list
           $prefix = 'themebox_met_';
  
           // Product Settings
           $header_settings = new_cmb2_box( array(
           'id'            =&gt; 'Extra_settings',
           'title'         =&gt; esc_html__( 'Extra Settings', 'themebox' ),
           'object_types'  =&gt; array( 'product'), // Post type
           'context'       =&gt; 'normal',
           'priority'      =&gt; 'high',
           'show_names'    =&gt; true,
  
             ) );
  
           $header_settings-&gt;add_field( array(
          'name'       =&gt; esc_html__( 'Add Image Detail size 590x300 px', 'themebox' ),
          'id'         =&gt; $prefix . 'img_detail',
          'type'             =&gt; 'file'
      ) );
  
       }
  </code></pre>
  
  <p>I want to add this custom image upload field in template form new-product.php and when save form in dokan 
  the image upload custom field update with an image added in dokan .....exactly like featured product image in WooCommerce</p>