urisourcebin: extend statistics to include number of queues
Copied from https://gitlab.freedesktop.org//gstreamer/gst-plugins-base/-/merge_requests/1194
At the application level, we can't know whether the current URI required queuing at all, and judging by the code it isn't trivial to figure it out.
Adding the number of queues to the statistics makes it possible to determine that there is no cause for alarm when all the levels are at 0 (eg file://)