Add support of json-mode to chatgpt node

The idea is:

We need to ask chatgpt for content, that should be parsed as json. https://platform.openai.com/docs/guides/text-generation/json-mode
Recently OpenAI added special option to provide ansvers in json\xml.

My use case:

I generate content with chatgpt, but it is a set of tags and properties (result of classification). To parse those answer, we ask chatgpt to output them in json.
The new option simplifies that flow, reducing the amount of invalid jsons in the output.

Any resources to support this?

(https://platform.openai.com/docs/guides/text-generation/json-mode)

This will be added as part of the overhaul we are doing on the OpenAI node, You can find the PR with the changes here: feat(OpenAI Node): Overhaul by michael-radency · Pull Request #8335 · n8n-io/n8n · GitHub if you wanted to take a look at what we are doing.