needflows: Child needs as "part of parent-needs

[danwos]

Like need-parts, also child-needs should be included inside their parent-needs for needflows.

Example of need-part integration:

Maybe an option would be good, to define the parent-needs which are using this mechanism, maybe by filter-string.

https://sphinx-needs.readthedocs.io/en/latest/directives/needflow.html

Example:

.. req: ABC

   .. req: DEF
   
      .. spec:: Solving ABC and DEF
      
      
      .. test:: Test case for ABC and DEF 

Image should be:

ABC[DEF[SPEC + TEST ]] as image ;)

Output example:

[PhilipPartsch]

How shall the config parameter be named? Is the default behaviour to render the child needs inside or shall the default behaviour be the other way around?