Implement ClusterAddonCreate controller

Created by: janiskemper

Description

This controller is responsible for creating ClusterAddon objects. There is one ClusterAddon object for each Cluster.

This controller reacts on the create event of a Cluster and creates a corresponding ClusterAddon with the relevant owner reference and cluster reference set to the Cluster object.

In this way, we make it possible to automatically apply the cluster addons in each workload cluster that the user creates.