Omit config child if argument class protected

[mhdirkse]

I made this draft because I want to address two points:

• It may be better to implement this another way. I can omit methods from the config child candidate methods instead of omitting the config child.
• I need to document this in README.md and in the FRANKDOC.md of the iaf project.

[mhdirkse]

Please merge https://github.com/ibissource/iaf/pull/3320 as well to complete the documentation.