Enhance Flow Exporters

[lucaderi]

In the flow exporters probe page lua/pro/enterprise/nprobe.lua, it would be nice to see how many interfaces are being monitored per nprobe instance as well as in the exporters page, how many interfaces per exporter, like in the images attached. The graphic above the table on those pages seems to indicate number of interfaces for each exporter but it's so squished together that it's not that usable. It would be nice to have it in the table to be able to sort by.