feature request: set the level of formality for the translations

[markusmilkereit]

DeepL knows a couple of different "formality" levels, and modern branding voices are not always following the default "formal" setting.

Applied to the API call it looks like this, just don't know where you would want the setting to come from, maybe the Contao backend "settings"? Or the config.yml?

\contao-deepl\src\Api\DeepLApi.php line 36:
$this->translator = new Translator($this->apiKey, [TranslateTextOptions::FORMALITY => 'less']);

All formality options here: https://developers.deepl.com/docs/api-reference/translate
Can provide a PR with the change, just wanted to agree on where the setting should be :)