Integrate with the ChatGPT API as a new integration method

[micz]

Implement the integration with the ChatGPT API as a new method to use this addon, to be enabled in the options, using an API Key.

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Originally posted by @AI4everr in #12 (comment)

Instant Reply Integration: Thunderbird AI swiftly inserts replies into email windows, bypassing manual steps.

Your response:
Instant Reply Integration: To accomplish this, using the ChatGTP API is necessary, but it is a pay-per-use service.
I couldn't find an email anywhere, so I'm replying here if that's okay.

A paid service is not an issue; I currently use ChatGPT's paid service as well. It would be great if I could input my API key into your software to respond directly in the email window.

[e-gaulue]

@micz I saw you did a pull request on ali-raheem/Aify#9. Would be great if your extension could support at least openAI API.

Regards,