setup: Look for the authentication.ini instead of the config.ini

The config.ini does not include any settings mandatory to operate
Icinga Web 2, but the authentication.ini does.

refs #8134

library/Icinga/Application/ApplicationBootstrap.php

@@ -407,7 +407,7 @@ abstract class ApplicationBootstrap
      */
     protected function loadSetupModuleIfNecessary()
     {
-        if (! @file_exists($this->config->resolvePath('config.ini'))) {
+        if (! @file_exists($this->config->resolvePath('authentication.ini'))) {
             $this->requiresSetup = true;
             $this->moduleManager->loadModule('setup');
         } elseif ($this->setupTokenExists()) {