Kube-system namespace should be labeled by KIM

[koala7659]

Description:

KIM should put and maintain the operator.kyma-project.io/managed-by: kyma label on the kube-system namespace of created Kyma Clusters

Implementation:

• Check with Gardener developers that we can put such label with any problems
• Implementation in KIM as part of Cluster Provisioning process

More info:
The label will be used by Kyma users building thier own's monitoring solutions ex with Dynatrace. They must be sure to not monitor any system namespace and we will advise them to use this label to exclude kube-system namespace from monitoring.

Relates to: kyma-project/community#922