Switch Unicorn k8s-sidecar image back to hardened variant

[mjnagel]

Describe what should be investigated or refactored

#2266 migrated to the "less hardened" image build for the k8s-sidecar due to some missing dependencies. When issues are resolved, switch back to the hardened image.

Ensure that the image starts up as expected and functions across all usage.

Additional context

Note that this image is present for both Grafana and Loki and their versions/variants should be kept in sync to ensure a smaller zarf package.