Some twig functions aren't aware of the currently active language

Hi,

First of all thanks for a great module, it works like a charm.
I do have a small feature request, it would be nice if the twig function 'site_setting_field(..)' was aware of the current language by default if no language code was provided.

Problem/Motivation

Some twig functions aren't aware of the current language right now.
Currently I have to inject the langcode to use it as follows:
{{ site_setting_field('[id]', '[field]', '[view_mode]', langcode) }}
Instead of ideally just:
{{ site_setting_field('[id]', '[field]') }}

That's because Drupal\site_settings\Twig\TwigExtension::singleSiteSettingsByNameAndField does the following:

if ($langcode && $site_setting->hasTranslation($langcode)) {
  $site_setting = $site_setting->getTranslation($langcode);
}

Proposed resolution

Let's make it so that if no langcode was provided, the current language id is given.
I suppose the above code snippet would have to become:

$langcode = $langcode ?? $this->languageManager->getCurrentLanguage()->getId();
if ($site_setting->hasTranslation($langcode)) {
  $site_setting = $site_setting->getTranslation($langcode);
}

(The language manager will need to be injected in the class still)