Streams operators docs DIAGRAMS (ticket only for diagrams)

In the resolution PR to https://github.com/akka/akka/issues/24572 we are moving towards "one page per operator", e.g. Flow.map gets it's own documentation page as do all other FileIO and all other Flow/Source/Sink operators.

We want to have an example for each of them, as well as an "marble" diagram (or similar) for each of them; we will require the help of the community to make the initial addition happen since there are quire a few operators.

We propose using draw.io for all the diagrams; We should provide a common set of "images" or at least an initially consistent style for them. This is one example of working on a map function image:

TODO: Propose a specific workflow how to add such diagrams. The resulting XML file, such as here: https://github.com/ktoso/akkamazing/blob/master/src/Flow-or-Source/map.xml should be stored right next to the actual png / svg that we generate.

TODO LIST ALL OPERATORS TO BE DOCUMENTED HERE