Ability to monitor NistMirrorTask failures

### Current Behavior

The task runs in the background.
If the task fails (e.g., network issue, NVD server down), there is no built-in alert or monitoring mechanism.
Failures can only be discovered by inspecting the logs.

### Proposed Behavior

Expose task execution status via API or UI.
Optionally, provide metrics or alerts when the task fails.
Enable integration with monitoring systems (e.g., Prometheus, email notifications).

### 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