Add cloudevents attribute (if missing) during the encoding process.

Add cloudevents extension (if missing) during the encoding process.

Delete cloudevents attribute during the encoding process.

Delete cloudevents extension during the encoding process.

Update cloudevents attribute (if present) using the provided function during the encoding process.

Update cloudevents extension (if present) using the provided function during the encoding process.

Returns a TransformerFactory that converts the event context version to the specified one.