Further Improvements for Cilium Alerts within KAS/AgentK

The features related to Cilium Alerts within KAS/Agentk has been implemented as part of two epics:

• Initial epic: &3438 (closed)
• Follow-up epic: &5041 (closed)

As a further improvement, there are some refactoring which could be done for improving performance or simplifying logic and code complexity.

Tasks:

• Refactor existsLabelsInEndpointSelector() to accept the EndpointSelector type instead of string
• Refactor Switch CiliumNetworkPolicies(ns).List(ctx, metav1.ListOptions{}) to an informer in order to avoid the expensive calls. Replacing List by Watch would be helpful already.

Related source code

• GitLab K8s Agent: https://gitlab.com/gitlab-org/cluster-integration/gitlab-agent/-/tree/master/internal/module/cilium_alert/agent
• Cilium Watch for network policies: https://github.com/cilium/cilium/blob/v1.9/pkg/k8s/client/clientset/versioned/typed/cilium.io/v2/ciliumnetworkpolicy.go#L46
• Cilium Informer for network policies: https://github.com/cilium/cilium/blob/v1.9/pkg/k8s/client/informers/externalversions/cilium.io/v2/ciliumnetworkpolicy.go#L35
• Informer implementation from within Kubernetes: https://github.com/kubernetes/client-go/blob/master/informers/generic.go