modify messaging implementors to transmit CloudEvents instead of bytes (i.e., list<u8>)

[danbugs]

Describe the solution you'd like
The event type should be the following:

    record event {
		specversion: string,
		ty: string,
		source: string,
		id: string,
		data: option<list<u8>>,
		datacontenttype: option<string>,
		dataschema: option<string>,
		subject: option<string>,
		time: option<string>,	
		extensions: option<list<tuple<string, string>>>
    }

Additional context
n/a