Cluster templates work out-of-the-box with managed networks (without provided network_id) #37

User Story

As a CAPSTK User I want:
cluster templates to work out-of-the-box with managed networks without having to provide STACKIT_NETWORK_ID

So that: I can spin up a fully working Kubernetes cluster with automatic network provisioning and a functional Cloud Controller Manager (CCM).

Context & Problem Statement

Currently, StackitCluster supports creating managed networks dynamically at runtime (#34). However, our cluster templates (templates/cluster-template*.yaml) deploy the STACKIT Cloud Controller Manager via a ClusterResourceSet, which embeds a static cloud.yaml (stackit-cloud-config).

Since stackit-cloud-controller-manager strictly requires loadBalancer.networkId to start, users cannot omit STACKIT_NETWORK_ID when using clusterctl generate cluster today.

Acceptance Criteria

• Users can deploy clusters using cluster templates without specifying STACKIT_NETWORK_ID.
• The deployed stackit-cloud-controller-manager receives the dynamically resolved network ID (from .status.network.id or .spec.network.id) and starts successfully.
• Services of type: LoadBalancer can successfully provision STACKIT load balancers in both BYO and managed network modes.

Potential Approaches / Ideas for Discussion

1. Controller-managed Secret for CRS (Management Cluster): CAPSK reconciles/updates the ClusterResourceSet Secret (containing stackit-cloud-config) on the management cluster once the network ID is known, letting CAPI's CRS handle the workload cluster sync.
   Example: CAPV

2. Workload-Cluster ConfigMap reconciliation: CAPSK directly reconciles/patches the stackit-cloud-config ConfigMap in kube-system of the workload cluster once the control plane is reachable.
   Example: CAPO

3. (Optional / External) CCM Auto-Discovery: Support omitting loadBalancer.networkId and auto-discovering it from node network interfaces/metadata directly within stackitcloud/cloud-provider-stackit.
   (Note: Requires change and a new release in the external CCM repository).
   Example: GCP, AWS, ...