Add support for the new /v3/languages API #89

Hi DeepL team,

I noticed that deepl-node still uses the deprecated /v2/languages endpoint in getSourceLanguages() and getTargetLanguages().

Since DeepL now recommends /v3/languages, are there any plans to support this endpoint in the Node.js SDK?

The new API provides useful information about language availability for specific resources, as well as feature support such as glossaries and formality.

I also noticed that the PHP SDK already supports the new endpoint.

It would be great to have similar functionality in deepl-node, ideally while maintaining backward compatibility with the existing methods.

Thanks!