feat(collectionagent): add the kubernetes kustomize casting

[Nageshbansal]

Features

• Adds the kubernetes/kustomize collection agent casting with two collector kinds: agent runs a DaemonSet on every node, deployment runs a cluster-scoped Deployment behind a service. The SigNoz Kubernetes views need both.
• Adds docs/examples/collectionagent/kubernetes/kustomize, one directory per kind.

Example

Both collectors in one casting file:

apiVersion: v1alpha1
kind: CollectionAgent
metadata:
  name: signoz
spec:
  deployment:
    mode: kubernetes
    flavor: kustomize
  collector:
    kind: agent
    spec:
      env:
        SIGNOZ_INGESTION_ENDPOINT: <signoz-host>
        K8S_CLUSTER_NAME: <cluster-name>
---
apiVersion: v1alpha1
kind: CollectionAgent
metadata:
  name: signoz
spec:
  deployment:
    mode: kubernetes
    flavor: kustomize
  collector:
    kind: deployment
    spec:
      env:
        SIGNOZ_INGESTION_ENDPOINT: <signoz-host>
        K8S_CLUSTER_NAME: <cluster-name>

Each kind pours its own root under pours/collectionagent/collector/<kind>/, and either kind can be declared on its own.

Related: https://github.com/SigNoz/platform-pod/issues/2754