[Request] Pass custom stdin to prompts

[egoist]

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there's no way to pass a custom stdin to @clack/prompts

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add an option for stdin

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[natemoo-re]

Hey, thanks for opening an issue! I'm finally working through the backlog here.

Seems like this should be a simple enough to add, just an oversight that this wasn't already exposed. This would also help us with tests. I'll try to get this added to the next minor release.