Missing cloud event adapter tests

[joelgerard]

We need a complete set of Event adapter tests to ensure that the various combinations of event types (Cloud Event, Binary Cloud Event, Legacy Event) against the different signature types (FUNCTION_SIGNATURE_TYPE=[cloudevent,event]) work.

Don't ship CEs without this in order to ensure backwards compatibility.

[grant]

Hi @juliehockett, @di,
It looks like this framework supports CloudEvents on GitHub but it's not published? Do we need to change something before publishing? Maybe you have context on this bug.

(Context: Looking over all the FFs)