These APIs require a measurement, permitting an additional optimization
to reduce the search space against the TSM index. Specifically, the
search key prefix is extended from `org+bucket` to
`org+bucket,\x00=<measurement>`
* MeasurementNames
* MeasurementTagKeys
* MeasurementTagValues
* Adds an api to the models package for efficiently parsing the
measurement tag (\x00) from a normalized series key
Stuart Carnie
Jonathan A. Sternberg