Provide information to the user that CSO does not find the cluster-stack locally in the local_mode=true

[michal-gubricky]

/kind feature

Describe the solution you'd like
Based on the discussion in SovereignCloudStack/cluster-stack-provider-openstack#100 (comment) change log message in fake GitHub client to inform the user that CSO/CSPO does not find the cluster-stack locally in the local_mode=true.