Exit with non-zero code if post-install audit fails

[IonBazan]

Fixes #11357 by adding a new ERROR_AUDIT_FAILED = 5 exit code used when running composer install --audit.

[Seldaek]

Thanks

[vtsykun]

Hi, this feature affect on composer create-project and composer require commands, we use this commands in out CI to deploy packages to our customers and now they fail with status code 5.

On the one hand, this feature is good for security, but it is also BC, if Composer following Backward Compatibility Promise between minor releases