Policy violation notifications based on the violation state

### Current Behavior

Lets assume we define 2 policies.

Policy 1:
violation state: fail
conditions: severity is CRITICAL

Policy 2:
violation state: warn
conditions: severity is HIGH

If we now setup a notification for policy violations we will receive notifications for both types of violations. My current use case would be something like: if polciy2 is violated just display the violation in the UI , if policy1 is violated send a notification. Currently we recieve notifications either for both policies or for none.

### Proposed Behavior

It would be nice to be able to configure a violation state for an alert or if notifications are enabled for one policy at all.

### 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