Improve error message when ClusterExtension ServiceAccount is missing

[thetechnick]

When creating a ClusterExtension with .spec.install.serviceAccount pointing to a non-existent ServiceAccount, Operatort Controller is showing a potentially misleading message in the condition status. (See in example below)

Kubernetes cluster unreachable: Get "https://10.96.0.1:443/version": should not be part of the message.

  - lastTransitionTime: "2024-09-16T15:20:44Z"
    message: 'Kubernetes cluster unreachable: Get "https://10.96.0.1:443/version":
      serviceaccounts "nginx" not found'
    observedGeneration: 2
    reason: InstallationFailed
    status: "False"
    type: Installed