[Request] Pass custom `stdin` to prompts

[egoist]

Is your feature request related to a problem? Please describe. A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

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

Describe the solution you'd like A clear and concise description of what you want to happen. add an option for stdin

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.

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