Create new form element(Dropdown) in drupal 8 ajax and set image from taxonomy term

ShipPackageFlowForm.php

<?php

namespace Drupal\ship_package\Form;

use Drupal\Core\Url;
use Drupal\Core\Ajax\AjaxResponse;
use Drupal\Core\Ajax\HtmlCommand;
use Drupal\taxonomy\Entity\Term;
use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Display the main dropdowns.
 *
 */
class ShipPackageFlowForm extends FormBase {

  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return 'ship_package_flow_form';
  }

  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['ship_nation'] = [
      '#title' => $this->t('Local or international ship'),
      '#type' => 'select',
      '#options' => [
        '1' => t('National'),
        '2' => t('International')
      ],
      '#required' => TRUE,
    ];  
    $terms = \Drupal::service('entity_type.manager')->getStorage("taxonomy_term")->loadTree('aerial_package_type', $parent = 0, $max_depth = 1, $load_entities = FALSE);
    $packageTypeParents = [];
    foreach ($terms as $term) {
      $packageTypeParents[$term->tid] = $term->name;
    }
    $form['aerial_package_type_parent'] = [
      '#title' => $this->t('Choose type of package'),
      '#type' => 'select',
      '#options' => $packageTypeParents,
      '#ajax' => [
        'callback' => '::getAerialPackageTypeOption',
      ],
      '#suffix' => '<div class="aerial-package-type-parent-image"></div>',
      '#required' => TRUE,
    ];

    $form['aerial_package_type_child_wrapper'] = [
      '#type' => 'container',
      '#attributes' => ['id' => 'aerial-package-type-child-wrapper'],
    ];
    $packageTypeParent = $form_state->getValue('aerial_package_type_parent');
    if ($packageTypeParent) {
      $terms = \Drupal::service('entity_type.manager')->getStorage("taxonomy_term")->loadTree('aerial_package_type', $packageTypeParent);
      $packageTypeChildren = [];
      foreach ($terms as $term) {
        $packageTypeChildren[$term->tid] = $term->name;
      }
      $form['aerial_package_type_child_wrapper']['aerial_package_type_child'] = [
        '#title' => $this->t('Choose type of article'),
        '#type' => 'select',
        '#options' => $packageTypeChildren,
        '#required' => TRUE,
      ];
    }

    $form['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Continue'),
    ];
    return $form;
  }

  /**
   * Form submission.
   *
   * @param array $form
   *   Form structure.
   * @param FormStateInterface $form_state
   *   Form state with all values.
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {

    $nation = $form_state->getValue('ship_nation');
    $packageTypeParent = $form_state->getValue('aerial_package_type_parent');
    $packageTypeChild = $form_state->getValue('aerial_package_type_child');
    $url = Url::fromRoute('entity.taxonomy_term.canonical', [
      'taxonomy_term' => $packageTypeParent
    ]);
    $paths = explode('/', $url->toString());
    end($paths);
    $key = key($paths); 
    $packageTypeParentAlias = $paths[$key];
    // @TODO: Improve: instead of fromUri use fromRoute and keep alias as well!.
    //$url = Url::fromRoute('node.add', ['node_type' => 'arial']);
    $url = Url::fromUri("internal:/carga/inicial/detalle?edit[field_aerial_package_type]=$packageTypeChild&edit[field_aerial_is_national]=$nation&paragraphs-tools-autoadd=node:field_aerial_detail:aerdet_package_$packageTypeParentAlias");
    return $form_state->setRedirectUrl($url);
  }

  /**
   * Implements callback for Ajax on aerial package type selection.
   *
   * @param array $form
   *   From render array.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   Current state of form.
   */
  function getAerialPackageTypeOption(array &$form, FormStateInterface $form_state) {
    $response = new AjaxResponse();
    $packageTypeParent = $form_state->getValue('aerial_package_type_parent');
    $packageTypeParentTerm = Term::load($packageTypeParent);
    $image = '';
    if (!empty($packageTypeParentTerm->field_image->entity)) {
      $image = [
        '#theme' => 'image_style',
        '#style_name' => 'thumbnail', ///< @TODO: TBD image style with themer.
        '#uri' => $packageTypeParentTerm->field_image->entity->getFileUri(),
      ];
    }

    $response->addCommand(new HtmlCommand('#aerial-package-type-child-wrapper', $form['aerial_package_type_child_wrapper']));
    $response->addCommand(new HtmlCommand('.aerial-package-type-parent-image', $image));
    $form_state->setRebuild(TRUE);
    return $response;
  }

}