DO NOT MERGE: Temporaly use custom gstreamer branch
ci: Move needed scripts from gst-ci to cerbero When GStreamer's CI triggers cerbero's CI it sets CI_GSTREAMER_URL and CI_GSTREAMER_REF_NAME in the env pointing to the repository and branch to build.
Use unified GStreamer repository Since all GStreamer recipes now share the same git directory, we have to use a lock to avoid multiple recipes doing the git checkout concurrently.
source: Take recipes_remotes value from config Config files have recipes_commits and recipes_remotes properties but only the former was actually used. Move the code handling this into the base class.