Drop kube-rbac-proxy container config for metrics

[Rohit-0505]

The PR removes the soon-to-be deprecated kube-rbac-proxy container dependency and replaces it with Controller-Runtime's built-in authn/authz for securing the metrics endpoint. This simplifies setup, enhances security, and follows the latest Kubebuilder best practices.

Key Changes

• Removed kube-rbac-proxy dependency.
• Enabled Controller-Runtime's built-in authentication & authorization for metrics.
• Enhanced cert-manager integration to secure metrics with TLS encryption.
• Added e2e tests to validate the metrics endpoint

Fixes #108

Ref for reviewer (The link below has the discussions and steps to be follwed)
kubernetes-sigs/kubebuilder#3907

[hardikdr]

@Rohit-0505 Thanks for the PR!
I see there are significant changes — have you been able to test them end-to-end?
Also, are these changes aligned with any other project within ironcore-dev (e.g., metal-operator)? If so, could you please link the related PR here?

[Rohit-0505]

@Rohit-0505 Thanks for the PR! I see there are significant changes — have you been able to test them end-to-end? Also, are these changes aligned with any other project within ironcore-dev (e.g., metal-operator)? If so, could you please link the related PR here?

To perform the e2e-test, I have followed the kubebuilder approach for testing the metrics endpoint validation, and a github workflow is also added in this PR for e2e-test
Here is the reference PR from metal-operator ironcore-dev/metal-operator#243

[hardikdr]

Thanks @Rohit-0505, the workflow is helpful.

[hardikdr]

Can you please resolve the conflicts with the main branch, and we are good to go then.

[Rohit-0505]

Can you please resolve the conflicts with the main branch, and we are good to go then.

PR is rebased and resolved all conflicts.