Add metric for primary votes on the primary proposal #1051
Description
Context
In filecoin-project/lotus#13359 (related to nv27 upgrade) we saw F3 stall and we believe the reason is that we didn't have sufficient QAP on the new post nv27 chain. Our overall participation metric looked fine, but that metric doesn't tell us what percentage of QAP was following the new chain, and we suspect due to only being lightly above the necessary 66.6% buffer to begin, we then were diluted as nodes were split attempting to finalize multiple chains.
One metric that would have helped is % votes on the primary proposal. This would have revealed right away what is going on (primary proposal not getting enough votes).
Done criteria
New metric that exposes percentage of power voting for strongest proposal per instance/phase/round.