only collect per aggMetric stats when in debug mode.
only collect per aggMetric stats when in debug mode.

The per AggMetric stats use a goroutine for each series that
runs a timer to collect stats. In a production environment with
man hundreds of thousands of series, the hundreds of thousands of
goroutines running every seconde will starve the CPU with
excessive context switches.

OOM-Killer/metrictank,replay/metrictank,raintank/metrictank,OOM-Killer/metrictank,raintank/metrictank,replay/metrictank,raintank/raintank-metric,replay/metrictank,raintank/raintank-metric,replay/metrictank,raintank/metrictank,OOM-Killer/metrictank,raintank/metrictank,raintank/raintank-metric