Make APIs self-documenting

[goloroden]

What is this feature about?

At https://docs.wolkenkit.io/ we have the documentation for wolkenkit itself, but the APIs of the wolkenkit applications do not yet have any documentation. We could use the landing page of the broker to provide some automatically generated documentation based on the metadata of the model. This could help us to get closer to a self-documenting API.

What needs to be done to implement this feature?

• [x] Define a way to document commands, events, …
• [x] Enhance the /v1/configuration.json route to contain these information
• [ ] Make the API shell consume these information and display them as a page