ClusterCIDR and ServiceCIDR are settings that are only used if at least
AllocateNodeCIDRs is set. The route controller requires in addition to
it for ConfigureCloudRoutes to be true as well. Since
AllocateNodeCIDRs is by default false, if guard the parsing of these
settings in order to not unnecessarily spam logs. Amend the
documentation of kube-controller-manager for the 2 settings to point
out the requirement of AllocateNodeCIDRs to be true as well
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