Add Helm chart for Kubernetes deployment

[pashok2398]

Summary

• Add a Helm chart for easy deployment to Kubernetes
• Configurable RBAC scope (ClusterRole or namespace-scoped Role)
• Optional ServiceMonitor for Prometheus Operator
• Authentication support via Secret or existing Secret
• Comprehensive values.yaml with documentation

Features

• Service Discovery: Discover Prometheus instances via K8s API with configurable selector and namespaces
• Manual Mode: Alternatively, specify Prometheus URLs directly
• RBAC Flexibility: ClusterRole for cluster-wide discovery, or Role for namespace-scoped
• ServiceMonitor: Optional support for Prometheus Operator
• Security: Non-root user, read-only filesystem, no privilege escalation

Testing

• Tested locally with kind cluster
• Deployed kube-prometheus-stack and verified metrics collection
• Validated with helm lint and helm template

Usage Examples

Basic installation with service discovery:

helm install cardinality-exporter ./charts/prometheus-cardinality-exporter \
  --namespace monitoring \
  --set config.selector="app.kubernetes.io/name=prometheus"

Namespace-scoped RBAC:

helm install cardinality-exporter ./charts/prometheus-cardinality-exporter \
  --set rbac.clusterScope=false \
  --set config.namespaces[0]=monitoring

With ServiceMonitor (Prometheus Operator):

helm install cardinality-exporter ./charts/prometheus-cardinality-exporter \
  --set serviceMonitor.enabled=true

[zl728]

@pashok2398 hey ! thanks very much for submitting this, it is a very useful feature indeed

however unfortunately in thought machine we do not use Helm and accepting this PR would mean that by default we would have to switch to it. we have to keep the tool up to date with third-party party version upgrades to mitigate security vulnerabilities and adhere the SLDC SLA for them.

I am happy to accept PR if you find a way to make installation via Helm optional and not as a breaking change