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

containers/prowler/Dockerfile

@@ -1,7 +1,7 @@
 # Prowler CIS scanner — slim build for Kubernetes, image, and IaC providers
 # Strips PowerShell (M365) and dashboard dependencies from upstream
 # Includes Trivy for image vulnerability and IaC scanning
-ARG CONTAINER_APP_VERSION=5.22.0
+ARG CONTAINER_APP_VERSION=5.23.0
 
 FROM python:3.12-slim-bookworm AS build