[FEAT] - Kubectl for syncing KubeConfig entries of managed clusters

[IvoGoman]

Priority

(Medium) I'm annoyed but I'll live

Description

With the implementation of #416 Greenhouse provides access to Kubeconfigs generated for the individual clusters.
In order to make the consumption of these KubeConfigs more convenient a new Kubectl plugin called cloudctl is to be implemented.

cloudctl should be able to

• connect with a Greenhouse Central cluster
• retrieve generated KubeConfigs
• sync the KubeConfigs as entries into a local KubeConfig file

The internally used plugin kubectl-sync can be renamed and open-sourced to fulfil these requirements

Reference Issues

#87 #416