management cluster admin user is hard-coded in SecurityStoreImpl and we bypass security check for it.
instead, the user should be configurable (like the management cluster password) and a regular
user (with "manage" permission) should be created instead.
From SecurityStoreImpl point of view, this will remove special case to handle this cluster admin user.
Warning about not changing the default cluster credentials will have to be moved from the SecurityStoreImpl
to either FileConfiguration (when reading the value from the conf) or ManagementServiceImpl