Histogram: percentile annotations

[leeoniya]

placeholder issue to figure out how we want to do this

• should we do it automatically? have a UI for toggle?
• will it always be ascending (low percentile on the left)
• are the percentile markers user-configurable or static at p75, p90, p95?
• if we have a native histogram response from a datasource, we're limited by the bucket resolution so the markers will be approximate since we're not aggregating raw data on the client.

cc @torkelo @ryantxu

[github-actions]

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