Monitoring extension

[GitGab19]

From @Fi3 Beyond MVP2 doc:

"Some mining pools aim to monitor their clients' mining devices in order to display any malfunctioning devices on their web app, which is hosted by the pool. This can be easily achieved by tracking the shares submitted by each device. However, Sv2 extended channels group all downstream channels into one upstream channel, making it impossible for the upstream to determine which mining device created a received share. On the other hand, Sv2 group channels are transparent and allow the upstream to identify which mining device created a received share. To translate between Sv1 (downstream) and Sv2 (upstream), we cannot use group channels as they assume that all mining devices in the group are HOM, but in Sv1, mining devices are not HOM. Therefore, we need a translator proxy to send monitoring data upstream, and to accomplish this, the Sv2 extension has been selected. We must define and implement this extension in both the SRI pool and the SRI (tproxy?)."

Since it will be the first protocol extension, we should work on that in a precise way, following the Protocol Extensions paragraph in specs.