Add support for OpenAI GPT-3

[rbenza]

The OpenAI GPT-3 API has even better translation quality compared to DeepL. Would be great if this service could also be included.

[Airsaid]

This is a good idea and I will support it in the next release.

[rbenza]

Nice, I've just made a donation for your great work with this plugin. It's really useful. Keep up the good work!

[Airsaid]

Thank you so much for your donation! It has been very helpful to me in the ongoing development of the project.

[rbenza]

Hi, any timeline on the new version? I could maybe create some time for a PR to support OpenAI. But only if you not already started the work otherwise would be waste of time :)

[Airsaid]

Sorry, I've been busy with other things lately. So, welcome PRs!

[Airsaid]

#118