Add missing fields in RuntimeCR to avoid manual Shoot-Spec adjustments: DNS settings, Kubernetes configuration (autoscaler, kubeControllerMgr, kubeAPIServer)

[tobiscr]

Description

Some clusters include special configuration settings or hyperscaler specific adjustments (related to DNS or individual hyperscaler configurations), usually applied by SREs manually.

Goal is to avoid any manual adjustments in Shoot-Spec and cover all configuration parameters in the RuntimeCR and let them manage by KIM. SREs should be enabled to use RuntimeCR as single point for adjusting the ShootSpec.

SRE provided us a list of common cases where manually the Shoot-Spec was adjusted: #407

• DNS configuration (e.g. coreDNS and nodeLocalDNS)
• Kubernetes configuration (e.g. clusterAutoscaler,kubeAPIServer or clusterControllerManager)
• Worker-pool controller (machineControllerManager)

AC:

• Implement the support for fields which were usually manually adjusted by SREs.
• Setup a call with SRE and clarify how the migration for each field will happen:
  • Clarify who will create the backup / restore logic
  • Agree on a strategy for step-wise migration and its timelines
  • Clarify if any further risks exist (service interruptions etc.)

Reasons

Add support for regularly manually adjusted fields to avoid manually applied misconfigurations.

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