code: func GetClusterConfigSchema(extensionSchema string) string {
  	var clusterConfigSchema string
  	if clusterConfigSchema == "" {
  		clusterConfigSchema = fmt.Sprintf(ClusterConfigSpecSchemaTemplate, "")
  	} else {
  		clusterConfigSchema = fmt.Sprintf(ClusterConfigSpecSchemaTemplate, ","+extensionSchema)
  	}
  	return fmt.Sprintf(V2SchemaTemplate, MetadataSchema, clusterConfigSchema, DefaultDefinitions)
  }
docs: // GetClusterConfigSchema returns the schema with optionally injected
  // schema for extensions.