feat: Add support for deploying K8s Agent as Helm Addon during cluster deployment

[vijayaraghavanr31]

What problem does this PR solve?:
This PR introduces support for deploying the Nutanix K8s Agent as a Helm-based addon as part of the cluster deployment workflow in the CAREN repository.

Key changes:

Added support for HelmAddon strategy in the K8s Registration Agent handler.

Updated handler logic to fetch and apply Helm chart configuration dynamically using the provided credentials.

Created unit tests to validate HelmAddon flow and error scenarios.

Ensured the agent’s credentials are handled securely through Kubernetes Secrets instead of directly passing via values.yaml.

This enhancement enables seamless installation of the K8s Agent via HelmReleaseProxy (HRP) and HelmChartProxy (HCP) without manual post-deployment intervention.

Motivation

Previously, the K8s Agent installation was not integrated into the cluster creation process and required manual setup.
By integrating it as an addon:

The K8s Agent will be automatically deployed during cluster provisioning.

Sensitive credentials are now secured using Kubernetes Secrets.

This aligns the agent deployment with other addon-based lifecycle management mechanisms.
Which issue(s) this PR fixes:
Fixes #

How Has This Been Tested?:
Verified K8s Agent deployment using the HelmAddon strategy.
Confirmed that:

Pre-install hooks execute as expected.

The secret is created and retained after installation.

Post-upgrade hooks are triggered correctly.

Added unit tests under k8sregistrationagent/handler_test.go

K8s agent documentation
Special notes for your reviewer:

Cluster class used for testing with konnector Agent:
ClusterConfigWIthKonnectorAgent.yaml

Cluster creation - with konnector agent secret and addon:
(devbox) vijayaraghavan.r@CQGK42CXL4 cluster-api-runtime-extensions-nutanix % kubectl apply -f /Users/vijayaraghavan.r/code/vijay/docs/clusteryamls/test/ClusterConfigWIthKonnectorAgent.yaml secret/nkp-vijay-test-cluster-29-pc-credentials created secret/nkp-vijay-test-cluster-29-pc-credentials-for-csi created secret/nkp-vijay-test-cluster-29-pc-credentials-for-konnector-agent created secret/nkp-vijay-test-cluster-29-image-registry-credentials created secret/global-nutanix-credentials created cluster.cluster.x-k8s.io/nkp-vijay-test-cluster-29 created configmap/kommander-bootstrap-configuration created secret/prism-central-metadata created

HelmChartProxy
`(devbox) vijayaraghavan.r@CQGK42CXL4 cluster-api-runtime-extensions-nutanix % kubectl get hcp konnector-agent-0199eb7b-6107-73a5-b257-aa86711fd583 -o yaml
apiVersion: addons.cluster.x-k8s.io/v1alpha1
kind: HelmChartProxy
metadata:
creationTimestamp: "2025-10-17T09:01:06Z"
finalizers:

• helmchartproxy.addons.cluster.x-k8s.io
  generation: 1
  name: konnector-agent-0199eb7b-6107-73a5-b257-aa86711fd583
  namespace: default
  ownerReferences:
• apiVersion: cluster.x-k8s.io/v1beta1
  kind: Cluster
  name: nkp-vijay-test-cluster-29
  uid: d3c523c6-f598-4760-9286-ce1e8ae8fcda
  resourceVersion: "19416"
  uid: 28266af0-9c08-4f52-be70-4ff7e1473afe
  spec:
  chartName: konnector-agent
  clusterSelector:
  matchLabels:
  cluster.x-k8s.io/cluster-name: nkp-vijay-test-cluster-29
  namespace: ntnx-system
  options:
  enableClientCache: false
  install:
  createNamespace: true
  timeout: 10m0s
  upgrade:
  maxHistory: 10
  releaseName: konnector-agent
  repoURL: oci://helm-repository.default.svc/charts
  tlsConfig:
  caSecret:
  name: helm-repository-tls
  namespace: default
  valuesTemplate: |-
  agent:
  name: konnector-agent
  image:
  repository: quay.io/karbon
  name: k8s-agent
  pc:
  port: 9440
  insecure: true #set this to true if PC does not have https enabled
  endpoint: pc.dev.nkp.sh # eg: ip or fqdn
  k8sClusterName: nkp-vijay-test-cluster-29
  k8sDistribution: NKP
  createSecret: false
  version: 1.3.0-rc.0
  status:
  conditions:
• lastTransitionTime: "2025-10-17T09:03:25Z"
  status: "True"
  type: Ready
• lastTransitionTime: "2025-10-17T09:03:25Z"
  status: "True"
  type: HelmReleaseProxiesReady
• lastTransitionTime: "2025-10-17T09:01:06Z"
  status: "True"
  type: HelmReleaseProxySpecsUpToDate
  matchingClusters:
• apiVersion: cluster.x-k8s.io/v1beta1
  kind: Cluster
  name: nkp-vijay-test-cluster-29
  namespace: default
  observedGeneration: 1
  (devbox) vijayaraghavan.r@CQGK42CXL4 cluster-api-runtime-extensions-nutanix %`

Cluster automatically onboarded in PC

cluster deletion:
(devbox) vijayaraghavan.r@CQGK42CXL4 cluster-api-runtime-extensions-nutanix % kubectl delete -f /Users/vijayaraghavan.r/code/vijay/docs/clusteryamls/test/1konnectorAgent.yaml secret "nkp-vijay-test-cluster-29-pc-credentials" deleted secret "nkp-vijay-test-cluster-29-pc-credentials-for-csi" deleted secret "nkp-vijay-test-cluster-29-pc-credentials-for-konnector-agent" deleted secret "nkp-vijay-test-cluster-29-image-registry-credentials" deleted secret "global-nutanix-credentials" deleted cluster.cluster.x-k8s.io "nkp-vijay-test-cluster-29" deleted configmap "kommander-bootstrap-configuration" deleted secret "prism-central-metadata" deleted

[manoj-nutanix]

replace K8s Registration Agent to Konnector Agent everywhere in the code, comment, docs, etc

[manoj-nutanix]

pkg/handlers/lifecycle/konnectoragent/handler.go still refers to K8s Registration Agent .. please modify it to Konnector Agent. And, rename this file's dir konnectoragent to konnector-agent or konnectorAgent for readability