fix(toolkit): scrutiny dialog should fail with no tty

[eladb]

If STDIN is not connected to a TTY (terminal), and scrutiny is enabled,
we expect the program to fail (exit with non-zero exit code).

This is especially important for CI/CD scenarios where you wouldn't want
to accidentally deploy changes that didn't pass a scrutiny check.

Fixes #1380

Tested manually.

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Pull Request Checklist

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Testing

• Unit test and/or integration test added
• Toolkit change?: integration tests manually executed (paste output to the PR description)
• Init template change?: coordinated update of integration tests (currently maintained in a private repo).

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• README: README and/or documentation topic updated
• jsdocs: All public APIs documented

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[rix0rrr]

Error will be confusing w/o tty.

Better just throw directly w/ a more descriptive error

[eladb]

@rix0rrr let me know if this looks better

[eladb]

@RomainMuller ping

[RomainMuller]

I'm wondering if this works as expected on Windows, and whether this would still work when people do something like yes | cdk deploy --require-approval or not... But it's a pretty good first step either way.

[mergify]

Thanks so much for taking the time to contribute to the AWS CDK ❤️

We will shortly assign someone to review this pull request and help get it
merged. In the meantime, please take a minute to make sure you follow this
checklist:

• PR title type(scope): text
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