add fake_reply parameter to GPT4All.generate()

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Describe your changes

add fake_reply parameter to GPT4All.generate()

Issue ticket number and link

https://github.com/nomic-ai/gpt4all/issues/1959

Checklist before requesting a review

• [x] I have performed a self-review of my code.
• [ ] If it is a core feature, I have added thorough tests.
• [ ] I have added thorough documentation for my code.
• [ ] I have tagged PR with relevant project labels. I acknowledge that a PR without labels may be dismissed.
• [ ] If this PR addresses a bug, I have provided both a screenshot/video of the original bug and the working solution.

Demo

Steps to Reproduce

Notes