Add a rep memory capacity alert for ADR021
Add a rep memory capacity alert for ADR021

To meet "smoothed cf.rep.CapacityRemainingMemory
/ cf.rep.CapacityTotalMemory of < 33%." Alert if:

 - Less than 33% of reps' advertised memory
   capacity is unused
 - AND when averaged across a whole two hours
 - AND when smoothed with Exponential Weighted
   Moving Average over a window of 5.

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf