remoting: make a gstreamer pipeline configurable

Allow a gstreamer pipeline to be configurable via an weston.ini. It is
necessary that source is appsrc, its name is "src", and sink name is
"sink" in pipeline. Also, remoting plugin ignore port and host
configuration if the gst-pipeline is specified.
2 jobs for remoting-gst-pipeline-configurable in 2 minutes and 23 seconds (queued for 29 seconds)
Status Job ID Name Coverage
  Container Prep
passed #409680
container_prep

00:00:43

 
  Build
passed #409681
build-native-meson

00:01:40