Some links/repos in the documentation were still pointing to old repositories, change to mono repository Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2982>
Closes https://gitlab.freedesktop.org/gstreamer/gst-docs/-/merge_requests/106/ Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1324>