Add HTTP REST / Webhook source and destination to Eventstream

[svelde]

At this moment, Eventstream has no support for ingesting messages via HTTP REST / Webhook (like an Azure Function HTTP trigger).

The same goes for egress to an HTTP REST / Webhook endpoint.

Supporting these endpoints opens many possibilities to integrate directly with external platforms, in real-time.

[svelde]

As a source, offer both consuming a 3rd party endpoint (where the Eventstream pulls data from) and providing an endpoint where 3rd party solutions push data to. That last variant should act like an HTTP-triggered function.