Validate flag-thresholds in consensus-health checker
As of yesterday, votes may contain flag-thresholds
lines like this one from moria1 (line breaks only added here):
flag-thresholds stable-uptime=693369
stable-mtbf=153249
fast-speed=40960
guard-wfu=94.669%
guard-tk=691200
guard-bw-inc-exits=174080
guard-bw-exc-exits=184320
enough-mtbf=1
The consensus-health checker can look at these values and warn if one of them gets too high or too low. What values should it consider normal, and when should it begin warning?