<div class="std-toolbar btn-group">
    <a data-toggle="ajax" href="/s/plugins/reload" class="btn btn-default">
        <span
            data-toggle="tooltip" title="" data-placement="left"
            data-original-title="Upload the plugin via FTP or some other protocol to the plugins directory then click this button to install/upgrade.">
            <i class="fa fa-cubes"></i> <span class="hidden-xs hidden-sm">Install/Upgrade Plugins</span>
        </span>
    </a>
</div>

'mautic_plugin_reload' => [
    'path'       => '/plugins/reload',
    'controller' => 'MauticPluginBundle:Plugin:reload',
],

/**
* Scans the addon bundles directly and loads bundles which are not registered to the database.
*
* @return JsonResponse
*/
public function reloadAction()
{
   if (!$this->get('mautic.security')->isGranted('plugin:plugins:manage')) {
       return $this->accessDenied();
   }

   $this->addFlash(
       $this->get('mautic.plugin.facade.reload')->reloadPlugins()
   );

   $viewParameters = [
       'page' => $this->get('session')->get('mautic.plugin.page'),
   ];

   // Refresh the index contents
   return $this->postActionRedirect(
       [
           略
       ]
   );
}

$ bin/console psysh --env=dev
>>> $container->get('mautic.plugin.facade.reload')
=> Mautic\PluginBundle\Facade\ReloadFacade {#4588}

class ReloadFacade
{
    private $pluginModel;
    private $reloadHelper;
    private $translator;

    public function __construct(PluginModel $pluginModel, ReloadHelper $reloadHelper, TranslatorInterface $translator)
    {
        $this->pluginModel  = $pluginModel;
        $this->reloadHelper = $reloadHelper;
        $this->translator   = $translator;
    }

    /**
     * This method finds all plguins that needs to be enabled, disabled, installed and updated
     * and do all those actions.
     *
     * Returns humanly understandable message about its doings.
     *
     * @return string
     */
    public function reloadPlugins()
    {
        $plugins                 = $this->pluginModel->getAllPluginsConfig();
        $pluginMetadata          = $this->pluginModel->getPluginsMetadata();
        $installedPlugins        = $this->pluginModel->getInstalledPlugins();
        $installedPluginTables   = $this->pluginModel->getInstalledPluginTables($pluginMetadata);
        $installedPluginsSchemas = $this->pluginModel->createPluginSchemas($installedPluginTables);
        $disabledPlugins         = $this->reloadHelper->disableMissingPlugins($plugins, $installedPlugins);
        $enabledPlugins          = $this->reloadHelper->enableFoundPlugins($plugins, $installedPlugins);
        $updatedPlugins          = $this->reloadHelper->updatePlugins($plugins, $installedPlugins, $pluginMetadata, $installedPluginsSchemas);
        $installedPlugins        = $this->reloadHelper->installPlugins($plugins, $installedPlugins, $pluginMetadata, $installedPluginsSchemas);
        $persist                 = array_values($disabledPlugins + $enabledPlugins + $updatedPlugins + $installedPlugins);

        if (!empty($persist)) {
            $this->pluginModel->saveEntities($persist);
        }

        // Alert the user to the number of additions
        return $this->translator->trans(
            'mautic.plugin.notice.reloaded',
            [
                '%added%'    => count($installedPlugins),
                '%disabled%' => count($disabledPlugins),
                '%updated%'  => count($updatedPlugins),
            ],
            'flashes'
        );
    }
}

'models' => [
    'mautic.plugin.model.plugin' => [
        'class'     => \Mautic\PluginBundle\Model\PluginModel::class,
        'arguments' => [
            'mautic.lead.model.field',
            'mautic.helper.core_parameters',
            'mautic.helper.bundle',
        ],
    ],

    'mautic.plugin.model.integration_entity' => [
        'class' => Mautic\PluginBundle\Model\IntegrationEntityModel::class,
    ],
],

class BundleHelper
{
    private $coreBundles   = [];
    private $pluginBundles = [];
    private $allBundles    = [];

    /**
     * BundleHelper constructor.
     */
    public function __construct(array $coreBundles, array $pluginBundles)
    {
        $this->coreBundles   = $coreBundles;
        $this->pluginBundles = $pluginBundles;
        $this->allBundles    = array_merge($coreBundles, $pluginBundles);
    }

'mautic.helper.bundle' => [
    'class'     => 'Mautic\CoreBundle\Helper\BundleHelper',
    'arguments' => [
        '%mautic.bundles%',
        '%mautic.plugin.bundles%',
    ],
],

$ bin/console debug:container --parameter=mautic.bundles
 ---------------- -----------------------------------------------------------------
  Parameter        Value
 ---------------- -----------------------------------------------------------------
  mautic.bundles   {"MauticCoreBundle":{"isPlugin":false,"base":"Core","bundle"...
 ---------------- -----------------------------------------------------------------

 $ bin/console debug:container --parameter=mautic.plugin.bundles
 ----------------------- -----------------------------------------------------------------
  Parameter               Value
 ----------------------- -----------------------------------------------------------------
  mautic.plugin.bundles   {"MauticOutlookBundle":{"isPlugin":true,"base":"MauticOutloo...
 ----------------------- -----------------------------------------------------------------