Use Dependency Injection on integration_chargebee module

Problem/Motivation

using direct drupal configuration.

 public function submitForm(array &$form, FormStateInterface $form_state) {
    $config = \Drupal::config('integration_chargebee.settings');

    $site_name = $config->get('integration_chargebee_api_site_name');

Steps to reproduce

integration_chargebee/src/Form all page using drupal config
\Drupal::config('')

Proposed resolution

use Dependency Injection