tracker-miner-fs: Preempt GStreamer registry file creation
Initialize gstreamer in tracker-miner-fs, mostly as a means to ensure the registry file is guaranteed to exist and be up-to-date when the tracker-extract-3 process gets to start up and require the use of GStreamer plugins.
Also, use GST_REGISTRY_UPDATE=no
envvar to ensure the extractor will not attempt any registry update in any case. This will avoid unwanted plugins from being initialized in place.