Support listening to cloud events in knative

[jthomas]

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This is a feature request...

Looking at the recent knative integration (#119) - this works great for actions listening to HTTP requests as it proxies between the HTTP request and the expected Web Action parameters/response.

This work could be extended to support listening to Cloud Events on Knative. This would allow those actions to be connected to knative event sources.

Digging around in how Cloud Event receivers work - they use an SDK which just listens on a HTTP port for the incoming events and decodes to an object, e.g. https://github.com/knative/eventing-sources/blob/master/cmd/event_display/main.go

We can just import the CloudEvents JS SDK to handle the HTTP transport and proxy the events to the handler functions. https://github.com/cloudevents/sdk-javascript

[jthomas]

CloudEvents JS SDK now has an example of using it to decode events: https://github.com/cloudevents/sdk-javascript#receiving-events