add diagram showing how to consume the journal api

[alexkli]

The journaling api doc could use a diagram showing how to consume the journal api.

It is non trivial and everyone who worked on our end on a journal client found it extremely helpful to have such a diagram since just the available textual documentation isn’t enough for getting a proper understanding. And the retry logic can be easily misunderstood from my experience.

Here is an example flow (petri-net) diagram: adobeio-journal-v2-diagram.zip

But don't take it literally - it is slightly out of date. An IO Events engineer should first ensure it is correct.

(The zip contains both visio sources and a png)

[kgera]

Thanks @alexkli will get it reviewed and then update.