Expiry date for ignore rules

What would you like to be added: Adding an optional expiry date for the ignore rules

Why is this needed: For example, there is a vulnerability on a package and it is valid. but the team needs a week to fix it. In those situations, we can have an expiry date for the ignore rules - so that it alerts again if the issue is not fixed.

Example

ignore:
   - vulnerability: CVE-2008-4318
      expiry: 2021-12-30 01:00:00 UTC