fix coredns serviceaccount to match kubernetes bootstrap rbac

The Kubernetes bootstrap creates a ClusterRoleBinding 'system:kube-dns'
that references ServiceAccount 'kube-dns' in 'kube-system'. However,
the coredns chart was using the 'default' ServiceAccount because
serviceAccount.create was not enabled.

This caused CoreDNS pods to fail with 'Failed to watch' errors after
restarts, as they lacked RBAC permissions to watch the Kubernetes API.

Configure the chart to create the 'kube-dns' ServiceAccount, which
matches the expected binding from Kubernetes bootstrap.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: mattia-eleuteri <mattia@hidora.io>
(cherry picked from commit 7320edd71d)

packages/system/coredns/values.yaml

@@ -6,3 +6,6 @@ coredns:
   k8sAppLabelOverride: kube-dns
   service:
     name: kube-dns
+  serviceAccount:
+    create: true
+    name: kube-dns