[APM] investigate using HDR for percentiles aggregations

[dgieselaar]

Per suggestion of the ES team, we should investigate using hdr for our percentiles aggregations as it would be more efficient for latency values.

https://www.elastic.co/guide/en/elasticsearch/reference/master/search-aggregations-metrics-percentile-aggregation.html#_hdr_histogram

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)