Brief overview:
TO configure tracking percentile metrics in rainerscript:
User would need to define:
- which percentile to track, such as [p50, p99, etc.]
- window size - note, this correlates directly with memory usage to
track the percentiles.
To track a value, user would call built-in function `percentile_observe()` in their configurations to
record an integer value, and percentile metrics would be emitted every
impstats interval.
