Get notified on filter search results changes

USER STORY:

As Jira user I want to get notified when search results in my filter change, so that I would know if any issues are added or leave the filter.

DESCRIPTION:

Currently users can subscribe to filters and get notified on certain dates.

This suggestion is to provide users with an option for the notifications to go out whenever the search results change(issues that match the filter conditions are added or removed).