configure: rename package from gst-rtsp to gst-rtsp-server
configure: rename package from gst-rtsp to gst-rtsp-server

To match git module name and avoid confusion with the
rtsp lib in gst-plugins-base and rtsp plugin in -good.

barisdemiray/gst-rtsp-server,hsteinhaus/gst-rtsp-server,thaytan/gst-rtsp-server,surround-io/gst-rtsp-server,barisdemiray/gst-rtsp-server,thaytan/gst-rtsp-server,hsteinhaus/gst-rtsp-server,Lachann/gst-rtsp-server,surround-io/gst-rtsp-server,barisdemiray/gst-rtsp-server,hsteinhaus/gst-rtsp-server,Lachann/gst-rtsp-server,surround-io/gst-rtsp-server,Lachann/gst-rtsp-server,thaytan/gst-rtsp-server