Extend Steering API documentation by adding relevant annotations and descriptions

Go through all the existing endpoints and check if the descriptions, type information and other is sufficient to understand for new developers users.

Example 1

Currently there are many endpoints which not clearly define their usage, parameters etc. For example @nuss recently asked the following:

In den POST/Put Requests zu den hosts gibt's ein Feld ownerIds, einen als 'required' markierten Array von Integers, bei dem ich nicht weiss, was ich da angeben soll.

Looking at the POST /hosts endpoint, there is a parameter ownerIds (array). But it is not clear what these owners are. A hint that this are User IDs could be helpful. I'm not sure how far annotations can solve that. Ideally there could be some additional written description. At last an example could help developers to better understand the endpoint usage. But example can be solved as part of #111 (closed).

Example 2

Another example endpoint which lead to confusion is POST /schedules. Here the description is missing crucial information what needs to be passed. Also the parameters section mentions No parameters even though there are mandatory parameters like the showIds. Also compare the same example in #111 (closed)