Add support for Deepl

@dehacker Not a lot of spare time at the moment but we will take a look when we can.

Just FYI, I published a simple DeepL provider module for the AI ecosystem right now: https://www.drupal.org/project/ai_provider_deepl.

My translation module (https://www.drupal.org/project/ai_translate_textfield), which has different approach than the AI Translate module, will be using it soon.

Thank you! I would actually like to refractor this module to work in a way we could use plugins for translation providers, kind of in the way the Translation Management Tool does. But this would require a complete new version. I'll take a look at your implementation that will help a lot.

@jhuhta @dehacker New module version with translation providers as contrib modules. Deepl already implemented in Auto Node Translate Deepl Provider