additionalUserData.data renders invalid cloud-config

[mikeruu]

What happened:
When using the additionalUserData.data in cloud-config format to pass cloud-init actions to an ubuntu server, cloud-init fails to run because of the formatting

	failed to unmarshal arbitrary cloud-init data: yaml: line 2: block sequence entries are not allowed in this context, please check if you put valid yaml data:
	users: - name: ubuntu
	  ssh_authorized_keys:
	    - ssh-rsa ...

What did you expect to happen:

The output should be in the correct yaml format:

	users: 
          - name: ubuntu
	     ssh_authorized_keys:
	     - ssh-rsa ....

How to reproduce it:

apiVersion: controlplane.cluster.x-k8s.io/v1alpha1
kind: RKE2ControlPlane
  metadata:
    name: management-cluster-control-plane
    namespace: default
  spec:
    agentConfig:
    format: cloud-config
    additionalUserData:
      data:
        users: |
          - name: ubuntu
            ssh_authorized_keys:
              - ssh-rsa ...

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

There was a similar issue #212 but it was closed so maybe I'm just doing it incorrectly, is there a working example that you can share?

Environment:
K3s: v1.31.2+k3s1
clusterctl --core "cluster-api:v1.8.5" --infrastructure "metal3:v1.8.3" --bootstrap "rke2:v0.9.0" --control-plane "rke2:v0.9.0"

• rke provider version: rke2:v0.9.0
• OS (e.g. from /etc/os-release): Ubuntu 22.04 LTS