feat(hetzner): fix cluster-autoscaler addon for Hetzner cloud provider

[bjornharrtell]

Summary

Two fixes to make the kops-managed cluster-autoscaler addon work correctly on Hetzner. Without these the addon is completely non-functional: the autoscaler pod cannot authenticate and node groups are never registered.

Fixes #18133
Fixes #18134

Also related to #17543 (original HCLOUD_TOKEN report).

Changes

1. Pass HCLOUD_TOKEN and HCLOUD_NETWORK to the autoscaler pod

File: upup/models/cloudup/resources/addons/cluster-autoscaler.addons.k8s.io/k8s-1.15.yaml.template

The addon template only had an env: block for AWS (AWS_REGION). Added an else if hetzner block that injects HCLOUD_TOKEN and HCLOUD_NETWORK from the hcloud secret in kube-system. This secret already exists because the CCM addon creates it — no new secrets are required.

2. Fix the --nodes flag format for Hetzner

File: upup/pkg/fi/cloudup/template_functions.go

GetClusterAutoscalerNodeGroups() was using ig.Name + "." + cluster.Name as the --nodes suffix for all non-GCE providers. This produces a 3-field format (min:max:name.cluster) that the Hetzner autoscaler cloud provider does not recognise.

Hetzner requires 5 fields: min:max:instanceType:region:name. Added a Hetzner branch that computes:

region := ig.Spec.Subnets[0]   // subnet name == Hetzner location, e.g. "hel1"
group.Other = fmt.Sprintf("%s:%s:%s", ig.Spec.MachineType, region, ig.Name)

Producing e.g. --nodes=1:5:cpx32:hel1:nodes-hel1.

Testing

Manually verified against a live Hetzner kops cluster (kops 1.35, Hetzner hel1). The generated addon manifest now contains the correct env vars and --nodes format, and the autoscaler pod authenticates and registers node groups successfully.

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