OCPNODE-3372: Remove omitempty from defaultRuntime as its handled in MCO with additional test cases

Author: ngopalak-redhat

machineconfiguration/v1/tests/containerruntimeconfigs.machineconfiguration.openshift.io/AAA_ungated.yaml

@@ -13,5 +13,4 @@ tests:
         apiVersion: machineconfiguration.openshift.io/v1
         kind: ContainerRuntimeConfig
         spec: 
-          containerRuntimeConfig:
-            defaultRuntime: crun
+          containerRuntimeConfig: {}

machineconfiguration/v1/types.go

@@ -850,7 +850,7 @@ type ContainerRuntimeConfiguration struct {
 	// When set to `crun`, OpenShift will use crun to execute the container
 	// When omitted, this means no opinion and the platform is left to choose a reasonable default,
 	// which is subject to change over time. Currently, the default is `crun`.
-	// +kubebuilder:validation:Enum=crun;runc
+	// +kubebuilder:validation:Enum=crun;runc;""
 	// +optional
 	DefaultRuntime ContainerRuntimeDefaultRuntime `json:"defaultRuntime,omitempty"`
 }