Documentation for DASF as a whole

Part of review for https://github.com/openjournals/joss-reviews/issues/4052

Right now it is quite hard to get a comprehensive overview of DASF. The page https://git.geomar.de/digital-earth/dasf has a very, very brief description that links to https://doi.org/10.5880/GFZ.1.4.2021.004 with (apparently) a short paper on DAFS that reads similar to the JOSS paper.

https://git.geomar.de/digital-earth/dasf/dasf-messaging-python and the other components has a bit more info on contributing and very, very brief usage info via minimal examples. However, they are too sparse since they just do "hello world" rather than demonstrating the advertised use case. Also, they don't cover interaction between the components. The links to digital earth and flood event explorer just include general descriptions of this application and don't show how DASF is used there.

The following items should be included in the documentation:

• A comprehensive documentation for DASF as a whole that is linked to from all the pages users might land on.
• A diagram showing the components and their interaction in a deployed application.
• A non-trivial example that shows how the components are supposed to be used when doing actual data analysis in distributed IT infrastructures.
• Ideally, a live example with a web GUI so that users can try it out right away (optional).
• Help on deployment in such a distributed IT infrastructure, for example Docker and docker-compose templates.

Generally, the documentation should give visitors all information and resources to make use of DASF. Currently I don't even understand the use case from the available material. Where does the "big data" part come into play? It just appears like a simple RPC framework from what is presented. This should be extended significantly.