NO-JIRA: Fix Infrastructure PlatformType comment

The comment for the config/v1/Infrastructure.Spec.PlatformSpec.Type was
outdated with respect to the consts defined for the PlatformType
typedef. Update.

Author: 2uasimojo

config/v1/types_infrastructure.go

@@ -302,9 +302,10 @@ type PlatformSpec struct {
 	// balancers, dynamic volume provisioning, machine creation and deletion, and
 	// other integrations are enabled. If None, no infrastructure automation is
 	// enabled. Allowed values are "AWS", "Azure", "BareMetal", "GCP", "Libvirt",
-	// "OpenStack", "VSphere", "oVirt", "KubeVirt", "EquinixMetal", "PowerVS",
-	// "AlibabaCloud", "Nutanix" and "None". Individual components may not support all platforms,
-	// and must handle unrecognized platforms as None if they do not support that platform.
+	// "OpenStack", "VSphere", "oVirt", "IBMCloud", "KubeVirt", "EquinixMetal",
+	// "PowerVS", "AlibabaCloud", "Nutanix", "External", and "None". Individual
+	// components may not support all platforms, and must handle unrecognized
+	// platforms as None if they do not support that platform.
 	//
 	// +unionDiscriminator
 	Type PlatformType `json:"type"`