Introduce default videosink/autosink options
requested to merge liu_ming50/gst-plugins-base:introduce-default-videosink-autosink-options into discontinued-for-monorepo
So the end users can choose the default videosink/autosink at build time. It now also supports pipelines as default videosink/autosink, if no options chosen by meson, the default values go to autoaudiosink and autovideosink, no functional changes in that case.
Signed-off-by: Ming Liu liu.ming50@gmail.com