Ability to create a policy condition based on "Attributed on" value.

### Current Behavior

Currently the conditions that can be used in creating a policy are limited.

### Proposed Behavior

Would be great to have the ability to create policy to flag project where there are vulnerabilities that have not been triaged in a specified timeframe. This could be done based on the "Attributed on" value from the vulnerabilities.

### Checklist

- [X] I have read and understand the [contributing guidelines](https://github.com/DependencyTrack/dependency-track/blob/master/CONTRIBUTING.md#filing-issues)
- [X] I have checked the [existing issues](https://github.com/DependencyTrack/dependency-track/issues) for whether this enhancement was already requested