Add support for setting a rank on a plugin feature

[danjenkins]

You can increase the rank of a decoder so that it takes precedence over others... think hardware decoder vs software...

gst_plugin_feature_set_rank

https://gstreamer.freedesktop.org/documentation/gstreamer/gstpluginfeature.html?gi-language=c

Would be great to be able to set a higher ranking on a hardware decoder/encoder...

https://gstreamer.freedesktop.org/documentation/tutorials/playback/hardware-accelerated-video-decoding.html?gi-language=c
https://developer.ridgerun.com/wiki/index.php/GStreamer_modify_the_elements_rank

[danjenkins]

I started working on this over at https://github.com/tinyzimmer/go-gst/compare/main...broadcastervc:go-gst:add-feature-rank?expand=1 but its untested for now