Tool for calculating waste caused by worker startup/shutdown

[jonnor]

Wanted for realistic cost projections, and possibly to tune scaling algorithm/decisions (especially hysteresis).
Should maybe part of the cost analysis (ref #46).

Could be returned as a ratio/percentage of time spent on processing versus startup/shutdown.

[jonnor]

Related to #84

[jonnor]

Even before we can calculate a precise ratio, an indication of the average and typical 'active time' for workers would be valuable, because we can assume boot/shutdown to be in certain ballparks (say 40 and 20 seconds).