Invalide source in the CloudEvents binding

The Java SDK sets the CloudEvents source to [`cdevents-sdk-java`](https://github.com/cdevents/sdk-java/blob/fd02e040a9cca093b6bf90b421366aaf7c7ec3a8/src/main/java/dev/cdevents/CDEventTypes.java#L1056).

That's no compliant with what the [spec](https://github.com/cdevents/spec/blob/v0.2.0/cloudevents-binding.md#source) requires. `source` should be set to the source value within the CDEvent.