Add duration_ms percentiles

Summary:
[This note](https://fb.workplace.com/notes/340378350526665/) shows how a quantile stat can be defined.  I'm moving `accounting.duration_ms*` over to this so we get quantiles for "free".

I can't figure out how to stop generating the all time percentiles.  I don't think they're useful and could be misleading in the future.

Differential Revision: D68840920

fbshipit-source-id: 1684783e7ec52afbce28f60bcb3147b3da873e64

Author: John Oxley

fb303/ExportType.h

@@ -128,6 +128,8 @@ struct QuantileConsts {
   static constexpr const std::array<double, 2> kP0_P100{{.0, 1}};
   static constexpr const std::array<double, 4> kP25_P50_P75_P95{
       {.25, 0.5, 0.75, 0.95}};
+  static constexpr const std::array<double, 5> kP25_P50_P75_P95_P99{
+      {.25, 0.5, 0.75, 0.95, 0.99}};
 };
 
 struct SlidingWindowPeriodConsts {