Add support to create and manage a "management cluster"

[jaxesn]

Currently eks-anywhere clusters are self-managed, the eks-anywhere objects and controller are installed in every cluster and users can interact with these objects to modify their cluster infrastructure. This may not be the desired setup for all organizations. We should introduce the ability for users to create a management cluster which can be used to managed their other clusters. This would also enable gitops based operations for all changes, including creation of, managed clusters.

• Add spec property to differentiate management and workload clusters #384
• Create Workload clusters using an existing Management cluster #386
• Modify ETCD controllers to support multiple clusters  #389
• Modify InstallAddon phase to skip installation of controllers when using existing management cluster #390
• Update GitOps repo file structure to support management cluster #355
• Update cluster controller logic to support management cluster #372
• Validation for management and workload cluster #518