Currently, all Magic Castle clusters built on MC Hub have the same `centos` sudoer username. However, as mentionned by @cmd-ntrf, having a sudoer username matching the username of the cluster's owner would be more user-friendly. For instance, `centos@somecluster.c3.ca` would become `fredfc@somecluster.c3.ca`. This change would only affect MC Hub deployments with SAML authentication enabled. Without SAML, authentication, we don't have access to the owner's username, so the sudoer username would remain `centos`. When making this change, MC Hub should also show the sudoer username associated with each cluster, as mentionned in https://github.com/ComputeCanada/mc-hub/issues/26.