Document and provide tooling for TDMetrics

FDB has an implementation of high resolution metrics that can be logged to an external cluster for later analysis. These have previously been useful when investigating short time-scale performance issues. There is currently no tooling nor documentation describing how to use TDMetrics, the key/value format in the cluster, nor any tooling available to process the results into something meaningful. Providing this would be a boon to anyone doing detailed performance investigations.

Start by locating FoundationDB's existing high-resolution TDMetrics implementation and determine how metrics are logged to an external cluster. Done means documenting usage and the cluster key/value format, and providing tooling that turns collected results into meaningful output for short-timescale performance investigations.

Written by the indexing model from the issue text.