allow user to exclude stats for each tube in metrics

[tsyber1an]

The use case required to avoid an export of stats for each tube. It is needed when there is only interest in common stats and number of tubes can significantly increase metrics size. This could happen, for instance, in my production system where we have over 500 tubes per each VMs. 6 VMs in total. By avoiding such an export, i can remove an extra load from prometheus.