Improve error if invalid CloudEvent in Message<string?, byte[]>.ToCloudEvent()

The extension method to create a CloudEvent from a kafka message currently throws an ArgumentException if the message is not a CloudEvent type event, or if the headers fail validation. This means that you need to interrogate the Exception if you wish to handle this type of poisonous message explicitly.

System.ArgumentException: Unknown CloudEvents spec version '0.1' (Parameter 'message')
at CloudNative.CloudEvents.Kafka.KafkaExtensions.ToCloudEvent(Message2 message, CloudEventFormatter formatter, IEnumerable1 extensionAttributes)
at CloudNative.CloudEvents.Kafka.KafkaExtensions.ToCloudEvent(Message2 message, CloudEventFormatter formatter, CloudEventAttribute[] extensionAttributes) at JustEat.OpaOrderEventsWorker.Worker.EventConsumer.CloudEventKafkaEventWorker1.ConsumeEvents(CancellationToken cancellationToken) in /_/src/Worker/EventConsumer/CloudEventKafkaEventWorker`1.cs:line 52

I think it would be worthwhile to create a custom Exception and throw this if the message is invalid.