Public API classes and methods should have doc comments

[jspenger]

All public facing API classes and methods should have doc comments. This is currently not the case, hence we have this issue.

In order to solve this task, we can split it into the following steps:

• [ ] First, diagnose which public classes have no docs. Post the list of classes / files here as a comment.
• [ ] Then, start writing doc comments for each of them.
• [ ] Finally, a review by @jonasspenger should confirm that the doc comments are good.

The results should be merged via a PR.

I suggest that @aversey first creates a list of all public classes that currently have no docs. There will also be non-private classes that should be private instead, please also mark these classes as private[portals].

Either @aversey, or @jonasspenger, or both can write the docs. I suggest also using co-pilot for this, as it helps with uniformity.