Use Ctrl+, as the standard keyboard shortcut to invoke KDE programs' "Configure <Program>" menu items. Right now there is no shortcut defined for this, which is a shame because having a standardized shortcut for it is really useful, and we actually have the opportunity to do so because our software uses KStandardActions for these kinds of things.
I chose Ctrl+, because that's the standard shortcut for all (and I do mean all) programs in the macOS world--a standard that has started to trickle into the Windows world as well, because there was previously no standard there. Might as well standardize on what's already a de facto standard elsewhere, to avoid throwing away people's muscle memory.