Add XML documentation to interfaces and classes

[bistok]

This pull request adds XML documentation to the interfaces and classes in the codebase to improve code readability and maintainability.

This is a work in progress. I think this add value to the code.

[kgrzybek]

Hi @bistok

I am not sure whether this kind of comments are needed. I assume they are generated, but most of the time code is self explanatory and these comments add no value. Moreover, they add noise and what is worse - need to be maintained, so there is a risk that will be out of sync with code.

I add comment only when:

• I cannot express some concept in code or it is very hard to do that (rare case)
• I need to make a hack (rare case)
• it a public API (for instance REST API Requests)

Of course I will listen other opinions about that.

[AlmarAubel]

I agree with @kgrzybek, i think it only adds value if it gives additional information. Occasionally, it's beneficial to include comments for a utility method, particularly to explain its usage or to provide examples detailing the input and output, especially in the case of complex algorithms.