component manager downward compatibility ( idf4/5 mdns)

[a2800276]

I have a component which has a dependency on `mdns`. In IDF version 4.x `mdns` is part of the IDF so it's a component dependency which needs to be resolved from CMake. Starting with IDF 5 it's a "proper", managed component.

I declared the dependency in both the component manager / yml and the `CMakeLists.txt` (PRIV_REQUIRES), hoping the build system will magically pick and choose, but it complains that it can't resolve the component manager dependency (obviously).

As a number of components moved out of the IDF with version 5, I'm wondering what the best way is to deal with the situation? Is there some hidden feature buried deep down in idy.py that I was too lazy to look at? Or would I just maintain distinct branches?