Add gstreamer1-plugin-openh264 subpackage with the openh264 plugin
    
    Previously, the whole contents of this package used to be part of the
    openh264 srpm, which was used to build both the openh264 library and the
    gstreamer openh264 plugin. All of which was built in koji, but hosted by
    Cisco on their servers.
    
    Now with the introduction of the "noopenh264" stub package in Fedora,
    we'll be able to build the gstreamer plugin as part of
    gstreamer1-plugins-bad-free again. The stub is used during build
    time, and gets replaced by the actual openh264 library package that's
    downloaded directly from Cisco on actual user systems.
    
    The binary package name used to be gstreamer1-plugin-openh264 and this
    commit keeps the exact same package name, so no obsoletes are needed.