Fixed AI Writer operation models

[NemeZZiZZ]

• latest supported models for OpenAI (as by ChatGPT recommendation);
• allowed custom model name - for any future variations.

[Nitwel]

I'm not against allowing allowOther but I'm not very fond of removing all the already existing options. Also, if you make changes like this, please add some sources on where you got these values/options from and where OpenAI is recommending these.

Last but not least, please resolve the merge conflicts so I can give this another review. 😄