add config option to turn off logging of successful connections

this commit adds a config option which can be added for the aggregator instances to avoid noisy logging of unmatched metrics in console.log, introduced in 4424e46.

In practice it's gigabytes of log-noise, because aggregator priints this warning for each unmatched metric received.
Might make sense to enable for debugging or with setups where only a fraction of metrics sent through aggregator, instead of it being used as a proxy for cache, hence the option.