[conf] Make OptionChild class copy_assignable, move_assignable
[conf] Make OptionChild class copy_assignable, move_assignable

Stores a pointer instead of reference in the class.

rpm-software-management/libdnf,rpm-software-management/libhif,hughsie/libhif,hughsie/libhif,rpm-software-management/libhif,rpm-software-management/libhif,rpm-software-management/libdnf,hughsie/libhif,hughsie/libhif,Conan-Kudo/libhif,Conan-Kudo/libhif,rpm-software-management/libdnf,Conan-Kudo/libhif,rpm-software-management/libdnf,Conan-Kudo/libhif,rpm-software-management/libhif