Add option to generator command to skip y/n input prompt

[danecando]

I have a setup script in my package.json and I needed to tweak it a little bit to have it consistently generate the edgeql-js client library.

{
"setup": "echo \"n\" | yarn edgeql-js --target cjs --output-dir node_modules/edgeql-js --force-overwrite && sleep 1"
}

Would be nice to have an option to skip the gitignore overwrite prompt. I can work on a PR sometime just don't want to take the time if it won't get merged.