[ai_translate] more flexibility

now we show the actual model used to translate:

Here you can now configure different prompts per language and diffferent model per language:

Added some code so the module now also supports not selecting a model (and falling back to the one selected in the AI default settings).

1 Rebased and checked all merge conflicts.
2 Re-tested (with openai and Mistral
Tested the following
- settings screen (als entity reference settings as the form is now TREE structure which resulted in that setting not working)
- actual translation (which now uses batch)
tested with
- openai
- mistral