Removing all gardener-related values

[dergeberl]

We should remove all gardener related settings/values in the helm chart.

Valid point. In this case, I suggest closing this PR and removing all gardener-related values in a new PR.
The gardener extension should be responsible for injecting all gardener-related values in its controller.
Originally posted by @timebertt in #87 (comment)

• Drop values related to gardener's generic token kubeconfig #89
• drop gardener monitoring config in this repository and move it to extension