Upgrade Prowler to 5.23.0, remove registry workaround (#336)

## Summary

- Upgrade Prowler from 5.22.0 to 5.23.0
- Remove the `enumerate-images` init container workaround from `cronjob-image-scan.yaml`
- Use native `--registry` and `--image-filter` flags now that upstream fix (PR prowler-cloud/prowler#10470) is released

The init container was a workaround for prowler-cloud/prowler#10457 where `--registry` args weren't forwarded to the provider constructor. We wrote the fix, it was merged, and v5.23.0 includes it.

## Test plan

- [ ] Build new container (`mise run container-release prowler 5.23.0`)
- [ ] Update kustomization.yaml with new image tag
- [ ] Sync prowler ArgoCD app from branch
- [ ] Manually trigger image scan job and verify `--registry` works natively
- [ ] Verify CIS and IaC scan cronjobs still work

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #336

service-versions.yaml

@@ -310,8 +310,8 @@ services:
 
   - name: prowler
     type: argocd
-    last-reviewed: 2026-03-24
-    current-version: "5.22.0"
+    last-reviewed: 2026-04-14
+    current-version: "5.23.0"
     upstream-source: https://github.com/prowler-cloud/prowler/releases
     notes: CIS Kubernetes Benchmark scanner; weekly CronJob on minikube-indri