Add spice-webdavd to guest-desktop-agents
    
    This package allows gnome-boxes (installed by default) to provide
    out-of-the-box Shared Folder support for Fedora guests.
    
    spice-webdavd is provided by https://src.fedoraproject.org/rpms/phodav
    
    See https://pagure.io/fedora-workstation/issue/309