Incorrect use of `@variants container` on response

[swallez]

ml.evaluate_data_frame response is a container, which isn't supported in metamodel.ts (variants is only defined on Interface).

elasticsearch-specification/specification/ml/evaluate_data_frame/MlEvaluateDataFrameResponse.ts

Lines 26 to 33 in bc30f1a

	/** @variants container */
	export class Response {
	body: {
	classification?: DataframeClassificationSummary
	outlier_detection?: DataframeOutlierDetectionSummary
	regression?: DataframeRegressionSummary
	}
	}

We should either

• formally support it for properties requests and responses and update metamodel.ts
• or change this class to use a value_body pointing to a container class and forbid @variants on requests and responses.