'bootstrap' => ['debug'],
'modules' => [
    'debug' => [
        'class' => 'yii\debug\Module',
        'panels' => [
            'elasticsearch' => [
                'class' => 'my\namespace\DebugPanel',
            ],
        ],
    ],
],

<?php

namespace mynamespace;

use craftbasePlugin;
use craftwebApplication;

class MyPlugin extends Plugin
{
    public function init()
    {
        Event::on(
            Application::class,
            Application::EVENT_BEFORE_REQUEST,
            function() {
                /** @var yiidebugModule */
                $debugModule = Craft::$app->getModule('debug');

                $debugModule->panels['mycustompanel'] = new DebugPanel(['module' => $debugModule]);
            }
        );
    }
}