Returns a metric and runs it, returning the generated data.

Metrics have no stored timeframe, so the window is determined by an optional absolute date range:

• start - range start in ISO 8601 format.
• end - range end in ISO 8601 format.
• timezone - IANA timezone the range is interpreted in (defaults to America/Chicago).

start and end must be supplied together. When omitted, the metric runs over the trailing four weeks.