Add clusterctl support

[christianang]

Now that clusterctl supports ipam providers via kubernetes-sigs/cluster-api#7288, some work needs to be done in this provider to integrate with the clusterctl changes.

This provider-contract doc covers everything that needs to be done, but a summary of what I think needs to happen is:

• A GitHub release of this IPAM provider.
• The GitHub release contains:
  • metadata.yaml
  • ipam-provider.yaml (generated from ./config/default probably with some automation)
• Update metadata.yamll to adhere to the latest cluster-api contract version

There may be more that needs to be done, but this should be a good starting point.

/kind feature

[schrej]

Implemented and available as initial pre-release: https://github.com/telekom/cluster-api-ipam-provider-in-cluster/releases/tag/v0.1.0-alpha.1

Thanks for the summary!