Prevent circular references in included documentation structures

[g-pavlov]

What would you like to be added:
#87 adds support for including a documentation structure into another documentations structure. Moreover, this can go on recursively. However, it is necessary to address a situation with possible circular inclusions and yield error an error.

Why is this needed / describe a real-world scenario:

Manifest A declares:

nodesSelector:
  path: manifestB

Manifest B declares:

nodesSelector:
  path: manifestA

and this cannot be resolved into a meaningful structure.

How to categorize this?:
/kind enhancement
/priority normal