kcm rootCA missing apiserver ca leads to kube-root-ca problem

1 Bug phenomenon：

1. The kcm(kube-controller-manager) rootCA is generated by manageServiceAccountCABundle in targerconfigcontroller, and this func will get kube-apiserver-server-ca cm first , and then use it and other two cm to generate kcm rootCA
2. when sometimes（very unlikely to happen , but i have met this just one time） the kube-apiserver-server-ca cm is missing, and the manageServiceAccountCABundle generate rootCA without kube-apiserver-server-ca , and finally the kcm leader holds the wrong rootCA， it will lead to the kube-root-ca problem in every pod, and the ocp release wil not work until i stop the wrong kcm leader

2 Bug fix:
2.1. this bug can be resolved by adding kube-apiserver-server-ca check in manageServiceAccountCABundle of targerconfigcontroller ,as follows
https://github.com/openshift/cluster-kube-controller-manager-operator/blob/4ca346ef97def3697f1aa0368c9b35459b9b2f59/pkg/operator/targetconfigcontroller/targetconfigcontroller.go#L706-L720

2.1 maybe like this , but this is not the best way to resolve this problem

2.3 this is also can be resolved by modifying the openshift library func CombineCABundleConfigMaps in resourcesynccontroller as
https://github.com/openshift/cluster-kube-controller-manager-operator/blob/4ca346ef97def3697f1aa0368c9b35459b9b2f59/vendor/github.com/openshift/library-go/pkg/operator/resourcesynccontroller/core.go#L17-L67

3 This is related to the openshift library-go issue # issue 1472 github.com/openshift/library-go missing key configmap

Start in pkg/operator/targetconfigcontroller/targetconfigcontroller.go at manageServiceAccountCABundle, then compare the behavior with vendor/github.com/openshift/library-go/pkg/operator/resourcesynccontroller/core.go and library-go issue #1472. Verify how a missing kube-apiserver-server-ca ConfigMap affects the generated root CA and inspect relevant existing controller tests. Done means the missing input cannot produce an incorrect root CA and the failure behavior is covered.