[DependencyTrack] Allow setting priorityClassName for API Server and Frontend

## Problem

The upstream `dependency-track` Helm chart does not support setting `priorityClassName` for the API Server StatefulSet or the Frontend Deployment. This prevents assigning Kubernetes PriorityClasses to these workloads natively via Helm values.

## Expected Behaviour

The chart should expose a `priorityClassName` value for both components:

```yaml
apiServer:
priorityClassName: ""

frontend:
priorityClassName: ""
```

This would allow users to assign a PriorityClass (e.g. `security-critical`) directly in `values.yaml`.

## Proposed Solution

Add `priorityClassName` to the pod spec templates of both the API Server `StatefulSet` and the Frontend `Deployment`, gated by an empty-string default so existing deployments are unaffected.

## Workaround

Currently users have to apply a manual `kubectl patch` or a post-deploy job to set `priorityClassName` on the resources after each deployment.