Update documentation for attribute age in scan result policies

What does this MR do and why?

This MR updates documentation for released feature (BE: Support new Age filtering options (#399116 - closed)).

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #399116 (closed)