Replace kube-rbac-proxy with controller-runtime built-in metrics auth

[slashpai]

Component(s)

Other (please comment)

What is missing? Please describe.

The operator currently uses kube-rbac-proxy as a sidecar to protect the /metrics endpoint.

Kubebuilder has discontinued kube-rbac-proxy from its default scaffolding starting with v3.15.0 due to:

• The gcr.io/kubebuilder/kube-rbac-proxy registry being deprecated (Google Container Registry shutdown)
• kube-rbac-proxy not yet being accepted under the Kubernetes umbrella
• controller-runtime now providing built-in metrics authentication and authorization

Image recently migrated to quay.io/brancz/kube-rbac-proxy:v0.21.0 (#336) for cve fixes but we need to follow kubebuilder recommendation for better dependency management and aligning with ecosystem.

Describe alternatives you've considered.

The recommended replacement is to use controller-runtime's SecureServing and WithAuthenticationAndAuthorization for the metrics endpoint, which the project already has available via controller-runtime v0.23.1.

Environment Information

Environment

Kubernetes Version: NA
Perses-Operator Version: v0.3.1