Unstake offline operators

[dariolina]

If an operator goes offline and does not unstake, their stake is still eligible for bundle author election. However, being offline, they do not produce bundles and decrease the domain’s throughput proportionally to their stake percentage.
We could use network pings and/or count the bundles produced by each operator to heuristically judge whether they may be offline and automatically unstake them (proposed algorithm)
This was discussed a while back, and we did mitigate it somewhat in #2215, but that does not solve the issue completely.