Refactor validation script

[stefanprodan]

The validation script should now work no matter the repo structure and its contents.

Improvements:

• Added CLI flags: New -d/--dir to set root directory and -e/--exclude to skip specific directories, replacing the hardcoded paths
• Added prerequisite checks: Verifies yq, kustomize, kubeconform, and curl are installed before running
• Auto-detection of non-Kubernetes directories: Automatically skips Terraform (.tf) and Helm Chart (Chart.yaml) directories from validation
• Downloads schemas from both flux2 and flux-operator releases, enabling validation of Flux Operator custom resources
• Broader kubeconform coverage: Validates all Kubernetes YAML files across the repo (excluding kustomize overlays and auto-detected non-K8s dirs), not just ./clusters with a depth limit of 2
• Hidden directory pruning: All find commands now skip dotfile directories (.github, .sops, etc.)
• Refactored from a flat script into functions

[matheuscscp]

LGTM