add metric for total number of participants in a conference, more documentation on metrics
add metric for total number of participants in a conference, more documentation on metrics

parlaylabs/jitsi-videobridge,davidertel/jitsi-videobridge,jitsi/jitsi-videobridge,davidertel/jitsi-videobridge,matteocampana/jitsi-videobridge,matteocampana/jitsi-videobridge,jitsi/jitsi-videobridge,davidertel/jitsi-videobridge,gpolitis/jitsi-videobridge,parlaylabs/jitsi-videobridge,jitsi/jitsi-videobridge,jitsi/jitsi-videobridge,jitsi/jitsi-videobridge,gpolitis/jitsi-videobridge,jitsi/jitsi-videobridge,gpolitis/jitsi-videobridge,parlaylabs/jitsi-videobridge,parlaylabs/jitsi-videobridge,matteocampana/jitsi-videobridge,jitsi/jitsi-videobridge