[plugins] Add example RHSM plugin
[plugins] Add example RHSM plugin

The plugin is rework of RHSM code from libdnf.
It has not yet been tested or compiled. It is in proof-of-concept state.

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