Support Capabilities.APIVersions in cluster addon helm charts

[chess-knight]

/kind feature

Describe the solution you'd like
[A clear and concise description of what you want to happen.]
As the cluster addon controller does helm template - #153, it doesn't include available API versions of the workload cluster. A similar problem with Capabilities.KubeVersion was resolved in #243.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]
It was discussed in #243 (comment).

Environment:

• cluster-stack-operator version:
• Kubernetes version: (use kubectl version)
• OS (e.g. from /etc/os-release):