`snyk test` with policy ignoring unreferenced item

[jabaran]

It is hard to keep .snyk policy files clean, it isn't always clear that an update has address something that was ignored.

I would like to see either through an option or general behavior that if the policy file is ignoring a snyk issue that the cli doesn't find a vulnerability for to ignore, this exit code results in an error explaining the the snyk policy specified is ignoring an unreferenced vulnerability.

Why? Since the cli ignores are not reported to ui, policy files need to be reviewed and having junk in the files makes reviews challenging.