OctoberCMS add fields under secondary tabs

Plugin.php

<?php 
class Plugin extends PluginBase
{
    public function boot()
    {
        parent::boot();
        $this->extendRainlabPost();
    }

    protected function extendRainlabPost() {
        Posts::extendFormFields(function (Form $form, $model, $context) {
            if (!$model instanceof \RainLab\Blog\Models\Post) {
                return;
            }
            $form->addSecondaryTabFields([
                'sticky' => [
                    'label' => 'Sticky post',
                    'type' => 'switch',
                    'tab' => 'rainlab.blog::lang.post.tab_manage'
                ]
            ]);
        });
    }
}