node: add better node autolink

Add node media, category and role properties and use those to select
the target node.
Tag the DSP node with the right media.class

src/examples/video-play.c

@@ -341,7 +341,11 @@ int main(int argc, char *argv[])
 	data.stream = pw_stream_new_simple(
 			pw_main_loop_get_loop(data.loop),
 			"video-play",
-			pw_properties_new("pipewire.client.reuse", "1", NULL),
+			pw_properties_new(
+				PW_NODE_PROP_MEDIA, "Video",
+				PW_NODE_PROP_CATEGORY, "Capture",
+				PW_NODE_PROP_ROLE, "Camera",
+				NULL),
 			&stream_events,
 			&data);