[release-v1.132] Automated cherry pick of gardener#13511: Add CustomDNSServerInNodeLocalDNS feature gate (gardener#13523)

* add ServerBlockSupportForNodeLocalDNS feature gate

* rename feature gate to CustomDNSServerInNodeLocalDNS

* address feedback

* address feedback

* Address PR review feedback from ialidzhikov (2)

* Update the feature gate version to 1.132

---------

Co-authored-by: docktofuture <sebastian.stauch@sap.com>

Author: ialidzhikov

docs/deployment/feature_gates.md

@@ -32,6 +32,7 @@ The following tables are a summary of the feature gates that you can set on diff
 | DoNotCopyBackupCredentials               | `true`  | `Beta`  | `1.123` |         |
 | OpenTelemetryCollector                   | `false` | `Alpha` | `1.124` |         |
 | UseUnifiedHTTPProxyPort                  | `false` | `Alpha` | `1.130` |         |
+| CustomDNSServerInNodeLocalDNS            | `true`  | `Beta`  | `1.132` |         |
 
 ## Feature Gates for Graduated or Deprecated Features
 
@@ -255,3 +256,4 @@ A *General Availability* (GA) feature is also referred to as a *stable* feature.
 | DoNotCopyBackupCredentials               | `gardenlet`                        | Disables the copying of Shoot infrastructure credentials as backup credentials when the Shoot is used as a ManagedSeed. Operators are responsible for providing the credentials for backup explicitly. Credentials that were already copied will be labeled with `secret.backup.gardener.cloud/status=previously-managed` and would have to be cleaned up by operators.                                                                                                                                                                                  |
 | OpenTelemetryCollector                   | `gardenlet`                        | Routes logs through an instance of an `OpenTelemetry Collector` in the control-plane of `Shoots`.                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
 | UseUnifiedHTTPProxyPort                  | `gardenlet`                        | Enables the gardenlet to set up the unified HTTP proxy network infrastructure. Gardenlet will also reconfigure the API server proxy and shoot VPN client to connect to the unified port using the new X-Gardener-Destination header.                                                                                                                                                                                                                                                                                                                     |
+| CustomDNSServerInNodeLocalDNS            | `gardenlet`                        | Enables custom server block support for NodeLocalDNS in the custom CoreDNS configuration of Shoot clusters.                                                                                                                                                                                                                                                                                                                                                                                                                                              |

pkg/component/networking/nodelocaldns/nodelocaldns.go

@@ -126,6 +126,8 @@ type Values struct {
 	Workers []gardencorev1beta1.Worker
 	// KubeProxyConfig is the kube-proxy configuration for the shoot.
 	KubeProxyConfig *gardencorev1beta1.KubeProxyConfig
+	// CustomDNSServerInNodeLocalDNS indicates whether server block support is enabled for node-local-dns.
+	CustomDNSServerInNodeLocalDNS bool
 }
 
 // New creates a new instance of DeployWaiter for node-local-dns.